A comparison of the effectiveness of cognitive behavioural interventions based on delivery features for elevated symptoms of depression in adolescents: A systematic review

Cognitive behavioural therapy is likely to reduce depression in young people, regardless of how it's delivered

Cognitive behavioural therapy (CBT) can be delivered in various ways, all of which are likely to reduce depression in young people. Self-help with therapist support is the most highly ranked, but the differences between the different types of therapy are small. It is unclear whether therapy delivered remotely (such as online) is effective.

Six to twelve months after treatment, self-help was the highest ranked for reducing depression. However, fewer types of delivery were tested over the long term, and there is no clear evidence of a difference between them.

No types of delivery are more acceptable to young people than any others.

What is this review about?

Depression is a common mental health problem in young people and is often treated with CBT. CBT is a talking therapy that aims to help people by changing negative patterns in the connections between thoughts, feelings and actions.

CBT can be delivered in different ways: face-to-face individually or in a group, via an app or website, using a book, remotely with a therapist online or on the phone or a combination of self-help and therapist support.

It is not clear which of these types of delivery are the most effective for young people.

What is the aim of this review?

This Campbell systematic review aims to collect information from studies of CBT for depression in young people to find out whether some delivery types are more effective than others for reducing depression, and whether any are more acceptable to young people.

What studies are included?

After searching for studies of CBT for depression in young people, 68 studies were included in the review. All studies are randomised controlled trials.

What are the main findings of this review?

Most types of CBT reduce depression in young people. Self-help with support from a therapist is the highest ranked for effectiveness, although the differences are small. We only found one study of CBT delivered remotely.

None of the delivery types are more effective than any others 6-12 months after treatment. Self-help CBT without therapist support is the highest ranking in the long term. No studies examined self-help with support from a therapist or CBT delivered remotely over the long term.

No delivery types are likely to be more acceptable to young people than any others.

What do the findings of this review mean?

All types of CBT are likely to reduce depression in young people, although more research is needed for remote CBT.

Self-help with therapist support is the highest ranked, but it was only tested with young people aged 16–19 years; the results may not apply to younger age groups.

Self-help without support is the highest ranked in the longer term. Further research is needed to learn whether self-help enables young people to maintain improvement and whether therapist support would further improve long-term outcomes.

How up-to-date is this review?

The review authors searched for studies up to November 2020.

Description of the condition

Depression is a public health problem and common amongst adolescents. In the UK, the rate of mental illness in young people has been rising in recent years and this is expected to continue, particularly due to the COVID-19 pandemic (The Lancet Child and Adolescent Health, 2021). The Mental Health of Children and Young People (MHCYP) Survey in England 2017 found that 2.1% of children and young people aged 5–19 have a depressive disorder, with the prevalence increasing with age to 4.8% in 17–19-year olds (NHS Digital, 2018). It is estimated that around one in ten adolescents in the US experiences at least one major depressive episode per year (CBHSQ, 2015). In Europe, the prevalence of depression in adolescents has been reported using baseline data from a randomised controlled trial, which found the prevalence ranging from 7.1% to 19.4% across 11 countries (Balázs, 2012). Research is ongoing to assess how the COVID-19 pandemic and related restrictions have affected young people's mental health, but a recent analysis indicates that the percentage of young people aged 11–16 years in England with a probable mental disorder increased from 12.6% in 2017 to 17.6% in 2020 (Vizard, 2020).

A diagnosis of major depressive disorder, according to the DSM-V criteria, is characterised by the presence of five or more symptoms, such as a persistent depressed mood, a loss of interest or pleasure in daily activities, sleep problems, change in appetite or weight, fatigue, feelings of worthlessness or guilt, diminished concentration, and suicidal thoughts, consistently for at least a 2-week period (American Psychiatric Association, 2013). Clinically significant distress or impairment in social, occupational, or other important areas of functioning must also be present.

The incidence of major depressive disorder in children and adolescents is associated with lifetime psychiatric comorbidity, risk of suicidality, functional impairments, and recurrence (Rohde, 2013). An analysis of global data found that neuropsychiatric disorders were the main cause of disease burden for young people aged 10–24 years, with most of these accounted for by unipolar depressive disorders (Gore, 2011).

In addition, a history of depressive episodes or elevated symptoms of depression are significant risk indicators of later major depressive disorder and can have a negative impact on quality of life (Bertha, 2013). An analysis from the Christchurch Health and Development Study birth cohort in New Zealand found that subthreshold depression in young people aged 17 to 18 years was associated with later depression and suicidal tendencies up to age 25 (Fergusson, 2005). However, a prospective longitudinal cohort study in Australia found that although diagnosis of depression in adolescence predicts diagnosis in young adulthood, the rates of disorder dropped by the late 20s (Patton, 2014). Remission was most likely in cases where adolescent depression was brief in duration. López-López (2020) analysed data from the Avon Longitudinal Study of Parents and Children (ALSPAC) in the UK and were able to distinguish five different trajectories of depressive symptoms. They found that clinically relevant symptoms at any age between 11 and 24 years, regardless of trajectory, are associated with poor education and employment outcomes in early adulthood, indicating that monitoring of symptoms over the course of adolescence is needed.

The evidence for the incidence, impact, and prognosis of adolescent depression continues to indicate that it is important to identify the most effective interventions to reduce depressive symptoms and limit the duration of diagnoses to improve quality of life in adolescence and into adulthood.

Description of the intervention

This review focusses on interventions that are based on cognitive behavioural therapy (CBT) and delivered through various modalities. CBT is widely used to treat depression amongst children, adolescents and adults and is one of several interventions recommended for treating depression in children and adolescents by the National Institute for Health and Care Excellence in the UK and the American Academy of Child and Adolescent Psychiatry in the US (Birmaher, 2007; NICE, 2017). CBT was also found to have the strongest evidence of clinical effectiveness in a review of digital health interventions for child and adolescent mental health, including for treatment of depression, with non-CBT digital health interventions having weaker evidence (Hollis, 2017).

CBT is a psychotherapy based on the premise that cognitions, behaviour patterns and emotions are linked, and that cognitive and behavioural techniques can produce changes in these links (Kendall, 1995). According to this model, adolescents with depressive symptomology have negative perceptions about themselves, the world and the future, which affect their behaviours and sustain their feelings of low self-esteem and hopelessness (Dobson, 2001). For example, depressed individuals will be selective in choosing the evidence for their performance, such that only those instances that support poor performance are remembered, which leads to behaviours that contribute to the development and persistence of depression, such as reduced engagement in activities. This diminished engagement reduces the chance of positive reinforcement. A reduction in positive reinforcement for healthy behaviours may lead to depressive symptomology, and depressed individuals often give up activities that they value. Thus, CBT aims to modify the relationship between thoughts, behaviours and emotions.

How the intervention might work

This review is concerned with examining various delivery modalities of CBT. CBT can be delivered by a therapist, whether in groups or individually, or through self-help. Therapist support may be delivered face-to-face or remotely via video or telephone calls or text messages with a therapist. Further, CBT can be delivered through web-based programmes that may or may not include communication with a therapist (Rathbone, 2017). Virtual appointments may improve accessibility to therapy and reduce costs. The dose (number, duration and frequency of sessions) of CBT varies and the dose–response relationship is not well understood (Girlanda, 2016).

Self-help delivery is independent of professional contact and can be delivered via books, computer programmes, or other media. The content and dose are often similar between face-to-face and remote therapy, although it may be more difficult to assess the amount of self-help content received as this relies on self-report or tracking through technology and uptake and engagement are likely to vary widely (Bergin, 2020; Fleming, 2018). Therapist support can be provided alongside self-help to guide the patient through the intervention (Cuijpers, 2010). Self-help CBT can be standardised (i.e., the material is not tailored to individuals and is the same package for all) or personalised (i.e., the material is tailored to individual needs), and it may or may not be interactive.

Digital technologies provide the potential to particularly increase access to treatments for young people, although rates of uptake and the cost-effectiveness of digital health interventions remains unclear (Hollis, 2017). A recent scoping review of preventive digital mental health interventions for children and young people found that most interventions were delivered in secondary schools and that mental health risk factors were not reported, which may indicate limitations of the reach and applicability of these interventions for young people at risk (Bergin, 2020). In the current COVID-19 pandemic, the need for remote delivery of mental health interventions has greatly increased, and NHS guidance has been provided to enable practitioners to conduct assessments and therapy remotely (NHS England, 2021).

Why it is important to do this review

Existing research does not provide clear conclusions regarding the relative effectiveness of the different delivery modalities of CBT for depression in children and adolescents. Amongst adults with depression, a previous network meta-analysis found no statistically significant differences between guided self-help, individual, group, and telephone delivery of CBT, and those formats were more effective than unguided self-help (Cuijpers, 2019). However, guided self-help was found to be less acceptable based on study drop-out.

A network meta-analysis of psychotherapies for depression in children and adolescents found that only interpersonal therapy and CBT were significantly more effective than control conditions and were more effective in reducing depressive symptoms than alternative psychotherapies such as play therapies and problem-solving therapy (Zhou, 2015). However, the review included different delivery modalities of each psychotherapy in the same node and therefore could not draw conclusions about the relative effectiveness of these modalities. Similarly, a recent systematic review of psychological treatments of subthreshold depression in children and adolescents included individual, group, and guided self-help interventions, finding a small to moderate effect on reducing depressive symptoms, but did not compare the effects of different delivery modes (Cuijpers, 2021).

A systematic review looking at the effectiveness of computerised therapies for anxiety and depression in children and young people identified studies testing three programmes for depression and two programmes aimed at both anxiety and depression; these included interactive games and standardised educational programmes (Pennant, 2015). All of the programmes for depression were rated by the authors as having low therapist input. One programme for depression and anxiety in the general population was rated as having low therapist input, but the remaining two programmes were for populations at risk of anxiety and depression and involved some therapist input. The review found that computerised CBT was more effective than non-therapeutic controls, but that face-to-face therapy was more effective than computerised CBT. A limitation of the review is that it looked at computerised therapies as a whole, rather than categorising them according to whether they were solely self-help interventions or included therapist support. Similarly, a review of online and social networking interventions for depression in young people found that online interventions with a cognitive behavioural focus were promising in terms of reducing depression (Rice, 2014). This review included studies with varying levels of support, usually from moderators or tutors. It also found a lot of variation between interventions in terms of dropout rates, and it was unclear whether level of support was related to attrition.

Another review that found computerised CBT interventions to be effective in reducing depressive symptoms in children and young people up to age 25 did not differentiate between therapist-guided and unguided self-help formats of CBT interventions (Ebert, 2015). Similarly, a review of computerised CBT for anxiety and depression found that included studies varied considerably in terms of therapist support (Richardson, 2010), and a review of internet-based CBT for children and adolescents found that most interventions involved some therapist support, mainly in the form of written messages or telephone calls (Vigerland, 2016). This is potentially important because there is some evidence based on an analysis of computerised psychotherapies with adults that the effect on depressive symptoms is moderated by the level of therapist support, with larger effects associated with therapist involvement (Andersson, 2009). A survey of young people using Child and Adolescent Mental Health Services in the UK also found that most young people would prefer to talk to a therapist, with only 9% preferring to use a computer programme on their own (Stallard, 2010).

Existing reviews are limited by the lack of primary research comparing the effectiveness of multiple modes of delivering CBT directly, with most studies comparing computerised forms of CBT (either purely self-help or self-help with therapist support) with waitlist, no treatment, or treatment as usual (TAU) controls (Calear, 2010; Fleming, 2014). While there are studies that compare the effectiveness of a particular mode of delivery of CBT to no intervention (e.g., van der Zanden, 2012) or another non-CBT control condition (e.g., Reynolds, 1986), few studies conduct a head-to-head evaluation of two different modes of delivering CBT. Existing reviews (Calear, 2010; Ebert, 2015; Fleming, 2014; Pennant, 2015; Rice, 2014) all combine self-help with therapist support and self-help without therapist report, making it impossible to determine the relative effectiveness of these two delivery modes and leaving open the question as to whether the addition of therapist support leads to greater effectiveness or patient engagement.

To address this gap, this review utilises network meta-analysis, a method that includes direct and indirect evidence of the relative effectiveness of different interventions and thus allows comparison of pairs of interventions where there are few or no studies that have tested the two interventions in a head-to-head trial. This method also allows for examination of the ranking probabilities of competing modes of delivering CBT based on their relative effectiveness for reducing depression amongst adolescents (Salanti, 2011).

Criteria for considering studies for this review

Types of interventions

The review included cognitive behavioural interventions that aimed to reduce symptoms of depression in adolescence, irrespective of delivery mode. For the purposes of this review, an intervention was considered a cognitive behavioural intervention if it included (1) evaluation of cognition to identify dysfunctional cognition, and (2) cognitive restructuring to adopt helpful cognition, and (3) a component focusing on behaviour: behavioural activation, problem-solving, social skills training or relaxation techniques. We recognised that variation in the third component may confound the estimated difference between treatment delivery modes, and that some interventions may have been partial CBT with more cognitive or more behavioural foci, but we were unable to identify these types of differences between the interventions from the descriptions provided in most studies (Hetrick, 2015).

If the description of the intervention in source documents was not adequate to make an assessment on inclusion based on the above criteria, the author(s) were contacted. If we did not receive further details from the author(s), we included studies that identified the intervention as CBT and excluded studies that did not identify the intervention as CBT.

Studies evaluating interventions that did not have all three CBT components listed above, or which were not identified by the authors as CBT, were excluded.

In line with the above conceptualisation of CBT, interventions such as acceptance and commitment therapy, mindfulness-based cognitive therapy and dialectical behaviour therapy that are rooted in principles different from those of CBT and focus on helping people to accept thoughts in a non-judgemental manner were excluded (e.g., Hayes, 1999; Linehan, 2006; Segal, 2012). Studies evaluating rational emotive behaviour therapy (REBT) were included as it is based in similar principles (Ellis, 2003).

Interventions were placed according to their mode of delivery into the following five categories: 1.

Therapist-delivered CBT in face-to-face individual sessions (individual CBT): CBT delivered by a therapist to individual clients in face-to-face sessions.

2.

Therapist-delivered CBT in group sessions (group CBT): This is similar to the above, but sessions are conducted for a group of clients rather than an individual client.

3.

Therapist-led CBT delivered remotely (remote CBT): This includes CBT that is delivered by a therapist remotely – for example, emails, video calls (e.g., Zoom) and text messaging. The delivery can be to individual clients or groups of clients.

4.

Unguided self-help (unguided self-help): This involves educating the client in the principles of CBT through reading material and helping them apply it through quizzes and activities. Traditionally, this was referred to as bibliotherapy and included workbooks. CBT can now be provided through various technological platforms (such as smartphone applications or browser-based programmes), and include audio files and videos in addition to text. When delivered electronically, self-help may include additional features such as reminders and some basic guidance on how to use the materials.

5.

Self-help with therapist support or guided self-help (guided self-help): This involves material to introduce and guide the client through CBT, alongside support from a therapist. For example, clients might gain an understanding of the approach to thoughts via the workbook and could be given homework and have regular feedback calls with a therapist.

Comparisons were classified as (1) no intervention, (2) TAU, and (3) placebo. To be included in the current review, studies must have done one of the following: 1.

Compared two cognitive behavioural interventions delivered through different delivery modes. Studies comparing two versions of cognitive behavioural interventions that have the same delivery mode were not included in the network meta-analyses. If such a study also has another relevant intervention or control group, the two different groups with a common delivery mode were considered as one intervention for the analysis. The way in which the common effect size were determined is explained below.

2.

Compared a cognitive behavioural intervention with a no intervention, placebo, services as usual control group. Comparisons in which any pharmacological treatment (e.g., antidepressants), complementary and alternative medicine (e.g., light therapy, acupuncture) or physical interventions (e.g., yoga, exercise) are explicitly provided (i.e., not as services as usual) were not considered because they are beyond the scope of this review. Waitlist controls were classified as no intervention controls. Services-as-usual were grouped together to avoid disconnecting the network. Psychological placebos may have included psychoeducation or attention placebos that were not expected to have any impact on the outcome of interest. Psychoeducation is the provision of information about a mental health condition without the provision of therapy. Attention placebo conditions provide similar time and attention from a therapist to participants without the provision of the active therapeutic intervention. Where services-as-usual or a placebo were not adequately described in source documents, the author(s) were contacted. If sufficient detail was not obtained, the study in question was excluded.

Studies where CBT was implemented in combination with another intervention were excluded unless the comparison group also received the additional intervention, meaning that the effects of the other intervention would be controlled for.

A sensitivity analysis separating therapist-led placebos, self-help placebos, and pill placebos was carried out.

We assumed that any adolescent who met the inclusion criteria was, in principle, equally likely to be randomised to any of the eligible interventions.

Figure 1 shows all possible intervention and control comparisons.

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Figure 1

Draft network including all treatment and control nodes.

Search methods for identification of studies

Data collection and analysis

Selection of studies

All references were screened for relevance by title and abstract by two members of the team independently, at least one of whom was an author (G. B., N. A., L. F., or S. S.). Screening and data extraction were managed and stored using Covidence.

The full text of potentially relevant articles was also screened independently by two members of the team (G. B., N. A., L. F., or S. S.) for inclusion. Discrepancies were resolved by consensus and discussion between three authors (G. B., N. A., and S. S.). Eligibility was assessed with reference to a pre-designed form based on the inclusion criteria. Studies excluded at this stage and reasons for exclusion are presented in Excluded studies. The PRISMA flow chart is presented as Figure 2.

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Figure 2

PRISMA flow chart.

The screening checklist included: 1.

Does the study include a relevant intervention? a.

Is the intervention based on CBT?

b.

Does the intervention target depression?

2.

Is the study conducted with adolescents, or students in secondary, middle or high school, or is the mean age between 10 and 19 years? a.

Specify mean age

3.

Is the study conducted with participants who have elevated levels of depression? a.

Specify screening measure and cut-off score

4.

Is the study an RCT with two different nodes in the network? a.

Confirm if RCT

b.

Specify all groups and potential nodes

Description of studies

Included studies

Table 2 provides an overview of the studies included in the review.

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Table 2

Characteristics of included studies.

References	Nodes	Number randomly assigned to each group	Inclusion criteria	Mean age (Age range)	Additional characteristics	Country (language)	Setting	Dosage	Outcome measure	Mean baseline scores (SD)	Follow-up Points (in months)	Type of Publication	Funding Source
Ackerson (1998)	None; Unguided (not interactive)	10; 12	CDI > 10; HRSD > 10	15.9 (14–18)		USA (English)	Home	N/A; Completed during own time over 4 weeks	CDI	16.8 (4.5); 19.7 (7.1)		Published	Not reported
Alavi (2013)	TAU; Individual	15; 15	MDD/suicide attempt in last 90 days	16 (12–18)		Iran (English)	Clinical	NR; 12-weekly sessions	BDI	27.78 (4.11); 30.58 (5.35)		Published	Shiraz University of Medical Sciences (Iran)
Araki (2019)	Placebo (self-help); Guided (not interactive)	65; 69	None	19.5 (NR)	College students	Japan (English)	College/University	1 90-min group session and 2 months no follow up; 1 90-min group session and 2 months of follow-up homework exercises	CES-D	23 (12.4); 19.7 (9.6)		Published	Not reported
Bella-Awusah (2016)a	None; Group	20; 20	BDI > 18	15.6 (14–17)		Nigeria (English)	School	N/A; 5-weekly 45- to 60-minute sessions	BDI, SMFQ	24.2, 11.8 (6.1, 2.7); 25.3, 13.4 (8.8, 4.5)		Published	John D and Catherine T MacArthur Foundation (USA)
Brent (1997)	Placebo (supported); Individual	35; 37	BDI > 13	15.6 (13–18)	MDD per DSM-III	USA (English)	Primary Care	NR; 12 to 16 approximately 1-h-weekly sessions followed by 2 to 4 monthly booster session phase: 2-4 sessions	BDI	25.7 (7.8); 24.3 (8.1)		Published	National Institute of Mental Health (USA)
Briere (2019)	Placebo (self-help); Group	37; 37	CES-D > 20	15.5 (14–18)		Canada (English)	School	NR; 6-weekly 1-h sessions	CES-D	1.66 (0.39); 1.55 (0.37)		Published	Fonds de Recherche Québécois sur la Société et la Culture (Canada)
Charkhandeh (2016)	None; Individual	60; 65	CDI ≥ 20; DSM-IV-TR (MDD)	NR (12–17)		Iran (English)	Primary Care	N/A; 24 twice-weekly 90-min sessions	CDI	30.35 (5.45); 29.46 (5.47)		Published	Not reported
Clarke (1995)	TAU; Group	74; 76	CES-D > 20	15.3 (NR)		USA (English)	NR	NR; 15 thrice-weekly 45-min sesisons	CES-D	21.88 (9.2); 24.29 (9.6)	12	Published	National Institute of Mental Health (USA)
Clarke (1999)	None; Group	27; 37	DSM-III-R (MDD or dysthemia)	16.2 (14–18)		USA (English)	Clinical	N/A; 16 twice-weekly 2-h sessions followed by 1 to 2 booster sessions	BDI	24.2 (10.8); 26.5 (9.4)		Published	National Institute of Mental Health (USA)
Clarke (2001)	TAU; Group	49; 45	DSM-III-R (MDD or dysthemia)	14.5 (13–18)		USA (English)	Clinical	NR; 13 1-h sessions	CES-D	23.8 (10.3); 25.2 (8.7)	12	Published	National Institute of Mental Health (USA)
Clarke (2002)	TAU; Group	47; 41	DMS-III-R	15.3 (13–18)	Major depressive disorder (MDD) or dysthemia per DSM-III-R	USA (English)	Primary Care	NR; 16 twice-weekly 2-h sessions	CES-D	34.2 (9.8); 33.5 (8.3)	12	Published	National Institute of Mental Health (USA)
Clarke (2016)	TAU; Individual	106; 106	DSM-IV-TR/K-SADS (MD)	14.6 (12–18)		USA (English)	Primary Care	NR; 2, 4-session modules (unclear on time frame of delivery), followed by monthly ph1 calls (up to 6 as required)	CES-D	27.96 (7.74); 28.34 (7.58)	9	Published	National Institute of Mental Health (USA)
Congleton (1996)	None; Group	5; 10	Systematic screening for behaviour disorders – teachers nominated students with internalising behaviour; CDI used but not for screening	13.5 (12–15)		USA (English)	School	N/A; 8 roughly twice-weekly 1-h sessions over 5 weeks	CDI (pretest), YSR – Depression (posttest)	48.2 (9.07); 49.4 (10.61)		Published	Not reported – PhD
Cui (2016)	Placebo (supported); None; Group	60; 60; 60	SDS >30, <56	19.42 (18–21)		China (English)	College/University	8 weekly, 2-h sessions; N/A; 8 weekly, 2-h sessions	SDS	43.82 (19.23); 43.64 (18.62); 44.14 (19.07)		Published	National Natural Science Project (China)
Curtis (1993)	None; Group	11; 12	BDI ≥ 16; DSM-III-R/CAS (MDD, dysthymia or adjustment disorder with depressed mood)	15.8 (NR)	Major depression, dysthymia, or adjustment disorder with depressed mood diagnosis per DSM-III-R	USA (English)	School	N/A; 12 roughly twice-weekly, 2-h after school sessions over an 8 week period	BDI, RADS	24.6 (6.4), 61 (3.8); 26.6 (10.2), 56.1 (13.4)		Unpublished	Not reported – PhD
De Cuyper (2004)	None; Group	11; 9	DSM-III-R (at least one criterion of MDD); CDI (cut-off score not reported)	10 (9–11)		Belgium (English)	NR	N/A; 16 1-h-weekly sessions followed by 2 booster sessions (1 and 4 months later)	CDI	15.27 (4.54); 12.67 (6)		Published	Not reported
Dobson (2010)	Placebo (supported); Group	21; 25	CES-D ≥ 24	15.2 (13– 18)		Canada (English)	School	15 sessions (length/frequency and duration unclear); 15 45-min sessions (frequency/duration unclear)	CDI, CES-D, MASQ-D	36.57 (5.34), 34.1 (11.08), 57.5 (15.09); 36.08 (5.63), 30.44 (7.02), 54.24 (14.05)		Published	Alberta Heritage Foundation for Medical Research (Canada)
Ede (2019)	None; Group	80; 82	CES-DC (moderate or severe clinical depression)	18 (16–21)		Nigeria (English)	College/University	N/A; 12-weekly 1-h sessions	CES-D	50.44 (7.68); 49.1 (6.25)		Published	Self-funded
Ettelson (2003)	None; Group	12; 13	DSM-IV	15.5 (14–18)	Major Depressive Disorder (MDD), Dysthymic Disorder (DD), or sub-clinical MDD per DSM0-IV	USA (English)	School	N/A; 16 twice-weekly 50 minute sessions over 8 weeks	CDI	63.25 (11.25); 69.31 (15.47)		Unpublished	Not reported – PhD
Fischer (1996)	Placebo (supported); Group	8; 8	BDI > 14	NR (12–17)	Detained adolescents at Detention Centre	USA (English)	Penal	5 90-min session 2× per week over 3 weeks; 5 90-min session 2× per week over 3 weeks	BDI	20.38 (8.2); 24.25 (10.34)		Unpublished	Not reported – PhD
Fleming (2012)	None; Unguided (interactive)	11; 19	CDRS-R ≥ 30	14.9 (13–16)		New Zealand (English)	School	N/A; 7 approximately 30-min modules completed at a rate of 1–2 modules/week over 5 weeks	CDRS-D, RADS	39.5 (NR), 70.5 (NR); 39.6 (NR), 70.3 (NR)		Published	New Zealand Ministry of Health; New Zealand Tertiary Education Commission
Gaete (2016)	None; Group	113; 229	BDI >10 (boys), >15 girls	15.9 (14–19)		Chile (English)	School	N/A; 8-weekly 45-min sessions	RADS	21.9 (8.5); 22.53 (9.53)		Published	Wellcome Trust (UK)
Garber (2009)	TAU; Group	157; 159	CES-D ≥ 20 or previous episode of MDD (DSM-IV)	14.8 (13–17)		USA (English)	Clinical	NR; 8-weekly 90 min sessions followed by 6 monthly 90-min continuation sessions	BDI	15.8 (10); 15.5 (9.4)	12	Published	National Institute of Mental Health (USA)
Hamamci (2006)	None; Group	11; 10	BDI ≥ 19; DAS (above average); ATQ (above average)	19.52 (NR)		Turkey (English)	College/University	N/A; 12-weekly 90-min sessions	CES-D	29.87 (8.5); 27.1 (7.32)		Published	Not reported
Idsoe (2019)a	TAU; Group	95; 133	BDI > 10	16.8 (15–18)		Norway (English)	Community	NR; 8-weekly 2-h sessions, or twice-weekly sessions over a shorted period, followed by 2 90-min	BDI	30.28 (10.67); 32.77 (8.8)	12	Published	The Research Council of Norway; Gidske og Peter Jacob Sørensens fond; Norwegian Directorate of Health
Ip (2016)	Placebo (self-help); Unguided (interactive)	127; 130	CESD-R >12, <40	14.6 (13–17)		Hong Kong (English)	School	NR; 10 modules, completed over 8 months at own pace	CES-D	20.43 (9.43); 20.66 (9.32)		Published	Lotteries Fund for Pilot Cyber Youth Outreaching Project (Hong Kong)
Kaesornsamut (2012)	None; Group	30; 30	CES-D >16, <29	16.9 (16–18)		Thailand (English)	School	N/A; 12-weekly 1-h sessions	CES-D	20.6 (3.44); 19.23 (2.78)		Published	Thailand Nursing and Midwifery Council
Kahn (1988)	None; Group	17; 17	RADS-I > 72; CDI	13.5 (10–14)		USA (English)	Clinical	N/A; 12 50-min sessions over 6 to 8 weeks	CES-D, RADS	28.46 (13.23), 86.91 (11.71); 26.53 (11.05), 85.41 (11.48)		Unpublished	University of Utah (USA)
Kennard (2006)	Placebo (pill); Individual	112; 111	CDRS-R > 45	14.6 (12–17)	Major depressive disorder (MDD) per DSM-IV	USA (English)	Primary Care	Medication; 14 twice-weekly 1-h sessions	CDI	81.26 (9.22); 78.69 (10.59)		Published	National Institute of Mental Health (USA)
Kerfoot (2004)a	TAU; Individual	23; 29	MFQ > 23	13.7 (NR)		UK (English)	Primary Care	NR; 8-weekly sessions	RADS	34.2 (8.3); 33.7 (8)		Published	National Health Service Executive (North West) (UK)
Kobak (2015)a	TAU; Individual	37; 39	QIDS-A-SR > 11	15.4 (12–17)	Mood disorder per DSM-V	USA (English)	School	NR; 12 weeks of treatment (frequency and length of sessions not stated) plus individualised text messages	RADS	NR (NR); NR (NR)		Published	National Institute of Mental Health (USA)
Lamb (1998)	None; Group	19; 27	RADS > 66	15.8 (14–19)		USA (English)	Community	N/A; 8 week long programme (frequency/length unclear)	MFQ	NR (NR); NR (NR)		Published	National Center for Nursing Research (USA)
Lewinsohn (1990)	None; Group	19; 21	DSM-III (MDD)/RDC (current episode of depressive disorder)	16 (14–18)	Major depression per DSM-III, current episode of minor depression per RDC	USA (English)	School	N/A; 14 twice-weekly 2-h sessions	BDI, CES-D	23.84 (11.43), 14.89 (4.3); 21.67 (11.34), 13.29 (5.21)	12	Published	National Institute of Mental Health (USA)
Listug-Lunde (2004)	TAU; Group	8; 9	CDI > 15	12.4 (NR)		USA (English)	Home	NR; 13 twice-weekly 35- to 40-min sessions for 7 weeks followed by 2 booster sessions within 1 month after treatment	CDI, CES-D	20.38 (4.1), 25.26 (11.72); 21 (4.95), 22.25 (8.51)		Unpublished	Not reported – PhD
Makarushka (2012)	Placebo (self-help); Unguided (interactive)	85; 76	CES-D > 13	12.7 (NR)		USA (English)	School	N/A; Completed during own time over 6 weeks at about 1 module per week	CES-D	27.19 (9.12); 26.91 (8.74)		Unpublished	National Institute of Mental Health (USA)
Marcotte (1993)	None; Group	13; 12	BDI > 15; HDRS > 10	15 (14– 17)		Canada (French)	School	N/A; 12 twice-weekly 45- to 60-min sessions	BDI	21.385 (6.33); 24 (8.2)		Published	Not reported
McLaughlin (2011)	TAU; Group	11; 11	BYI-II/CES-D (exhibited signs of depression)	11.82 (10–15)		USA (English)	Primary Care	NR; 10-weekly 50-min sessions	BDI, CES-D	49.73 (8.64), 18.64 (8.08); 57.18 (9.8), 20.18 (9.38)		Unpublished	Not reported – PhD
Merry (2012)	TAU; Unguided (interactive)	93; 94	PHQ-9/self-assessed (mild to moderate depressive disorder)	15.6 (12–19)		New Zealand (English)	Primary Care	NR; 7 modules completed during own time over 4- to 7-weeks	RADS	75.52 (14.42); 74.83 (13.35)		Published	New Zealand Ministry of Health
Moldenhauer (2004)	Placebo (supported); Individual	11; 15	CDI >15, <26	14.6 (12–17)		USA (English)	Primary Care	NR; 6 1-h-weekly sessions plus 6-weekly 45-min individual parent sessions	CDI	15.45 (7.03); 19.8 (9.47)		Unpublished	National Research Science Award; Sigma Theta Tau International; KM Donahue (USA)
Nelson (2003)	Remote; Individual	19; 19	DSM-IV (MDD)	10.3 (8–14)	Depression diagnosis per DSM-IV	USA (English)	Primary Care	6 1-h-weekly sessions plus 6-weekly 45-min individual parent sessions; 1 90-min session followed by 7-weekly 60-min sessions between the parent and the child	CDI	13.57 (9.85); 14.36 (8.75)		Published	Not reported – PhD
Parks (2013)	None; Unguided (not interactive)	18; 20	None	NR (NR); college freshmen	College freshmen	USA (English)	College/University	N/A; Over a period of 8 weeks	CES-D	18.8 (n/a); 19.5 (n/a)		Published	Not reported
Phillips (2005)	None; Group	31; 33	BDI > 10	17.7 (15–20)		USA (English)	School	N/A; 6 1-h-weekly sessions	BDI	18.65 (); 16.48 ()		Unpublished	Not reported – PhD
Rajabi (2018)	Placebo (supported); Group	10; 10	CDI > 22	NR (13–15)		Iran (Persian)	Education Counselling Centre	12 twice-weekly 90-min sessions; N/A	CDI	32.8 (NR); 29.2 (NR)		Published	Not reported
Reynolds (1986)	None; Group	10; 9	BDI > 12; RADS-I > 72; BID > 20	15.65 (NR)		USA (English)	School	10-weekly 50-min sessions; 16 twice-weekly 2-h sessions	BDI, RADS	16.9 (5.48), 80.7 (3.58); 21.11 (7.75), 85.67 (8.4)		Published	Wisconsin Alumni Research Foundation (USA)
Rohde (2006)	Placebo (supported); Group	48; 45	KSADS (MDD)	15.2 (13–17)	Juvenille Justice Referral; had conduct disorder	USA (English)	Penal	16 twice-weekly 2-h sessions followed by 2 optional sessions for parents; 6-weekly 1-h sessions with individual catch-ups when sessions were missed	BDI	15.4 (10.6); 16.6 (12.8)	12	Published	National Institute of Mental Health (USA)
Rohde (2014a)	TAU; Unguided (not interactive); Group	33; 22; 27	CES-D (endorsed two or more items)	19 (17–22)		USA (English)	School	6-weekly 1-h sessions with individual catch-ups when sessions were missed; NR; Completed during own time over 6 weeks	K-SADS	1.43 (0.35); 1.51 (0.41); 1.52 (0.39)	12	Published	National Institute of Health (USA)
Rohde (2014b)	TAU; Unguided (not interactive); Group	124; 128; 126	CES-D (endorsed two or more items)	15.5 (13–19)		USA (English)	College/University	NR; Completed during own time over 6 weeks; 6-weekly 1-h sessions with 10- to 15-minute individual catch-ups when sessions were missed	K-SADS	1.38 (0.36); 1.45 (0.41); 1.37 (0.35)	12	Published	National Institute of Health (USA)
Rossello (1999)	None; Individual	23; 25	DSM-IV(MDD or dysthymia)	14.7 (13–17)	Major depressive disorder (MDD) or dysthemia per DSM-III-R	Puerto Rico (English)	Clinical	N/A; 12 1-h-weekly sessions	CDI	20.13 (5.99); 20.12 (6.95)		Published	National Institute of Mental Health; University of Puerto Rico (USA)
Sanchez-Hernandez (2016)	None; Group	12; 13	CES-D (child) > 15	11.1 (10–12)		Spain (English)	NR	N/A; 12 twice-weekly 2-h sessions	CES-D	19.52 (8.03); 22.38 (6.54)		Published	University of Murcia (Spain)
Saranya (2017)	TAU; Guided (interactive)	42; 42	PHQ-9 >9, <19	17.7 (16–19)	Incarcerated	Thailand (English)	Penal Setting/Vocational Training	NR; 6-weekly 45- to 60-min sessions	PHQ-9	11.52 (2.73); 11.88 (2.86)		Published	Department of the Ministry of Justice (Thailand)
Saw (2019)	None; Group	10; 10	RADS-II > 76	16 (16)		Malaysia (English)	School	N/A; 8-weekly 90-min sessions	RADS	79.1 (3.67); 80.2 (4.83)		Published	Deanship of Scientific Research, King Fahn University; Global Asia 21st Century (Malaysia)
Saw (2020)	None; Group	43; 42	RADS-II > 76	16 (16)		Malaysia (English)	School	N/A; 8-weekly 1-h sessions	RADS	84.37 (4.68); 83.88 (4.6)		Published	Universiti Teknologi MARA; Ministry of Higher Education (Malaysia)
Sheffield (2006)a	None; Group	149; 134	CDI + CES-D score top 20%	14.34 (14–15)		Australia (English)	School	N/A; 8-weekly 90-min sessions	CDI, CES-D	23.3 (7.82), 30.24 (9.13); 21.3 (7), 27.55 (9.07)	12	Published	Not reported
Singhal (2018)a	Placebo (supported); Group	55; 65	CDI >14, <24	NR (13–18)		India (English)	School	45-min sessions (number/duration unclear); 8-weekly sessions (time not specified, but control was 45 min)	CDI, CES-D	21.8 (3.5), 29.5 (5.3); 22 (4.3), 29.4 (6.4)		Published	National Institute of Mental Health and Neuro Sciences (India)
Srivastava (2015)	TAU; Unguided (interactive)	10; 11	ICD-10 (mild/moderate unipolar depression)	16.5 (15–19)		India (English)	Primary Care	NR; 12-weekly sessions	BDI	24.3 (3.8); 26.4 (3.4)		Published	Indian Council of Medical Research
Stallard (2012)a	Placebo (supported); None; Group	374; 298; 392	SMFQ > 15	14.1 (12–16)		UK (English)	School	9 weekly or fortnightly 50- to 60-min sessions; N/A; 9 modules plus 2 booster sessions weekly or fortnightly 50- to 60-min sessions	SMFQ	10.6 (4.67); 10.56 (4.93); 10.64 (4.91)	6	Published	National Institute for Health Research (UK)
Stasiak (2014)	Placebo (self-help); Unguided (interactive)	17; 17	CDRS-R ≥ 30/RADS-II ≥ 76	15.2 (13–18)		New Zealand (English)	School	7 25- to 30-min modules over 4 to 10 weeks completed in own time; 7 25- to 30-min modules over 4 to 10 weeks completed in own time	RADS	66.12 (13.38); 77.47 (12.64)		Published	Not reported
Stice (2007)	Placebo (supported); Placebo (self-help); Unguided (not interactive); Group; None	19; 61; 28; 50; 67	CESD > 20; BDI < 30	18.4 (15–22)		USA (English)	School	4-weekly sessions; completed during own time over 4 weeks; completed during own time over 4 weeks; 4-weekly 1-h sessions; n/a	BDI	19.05(6.41); 19.95 (5.99); 20.28 (5.78); 20.58 (6.55); 19.38 (5.98)	6	Published	Hogg Foundation; National Institute of Health (USA)
Stice (2008)	Placebo (supported); TAU; Unguided(not interactive); Group	88; 84; 80; 89	CES-D > 20	15.6 (14–19)		New Zealand (English)	Primary Care	6-weekly 1-h sessions; NR; Completed during own time over 6 weeks; 6-weekly 1-h sessions	BDI	20.27 (9.83); 19.6 (9.23); 18.21 (7.53); 20.12 (10.38)	12	Published	National Institute of Health (USA)
Stikkelbroek (2020)	TAU; Individual	36; 34	KSADS (MDD)	16.6 (12–21)		The Netherlands (English)	Clinical	NR; 15 45-min-weekly sessions	CDI	24.1 (6.7); 27.1 (8.7)		Published	Dutch Organisation for Health Research and Development (Netherlands)
Topooco (2017)	Placebo (supported); Guided (interactive)	35; 35	BDI > 14	17.5 (15–19)		Sweden (English)	Clinical	NR; 8 Individual CBT modules and 8 individual therapy-weekly sessions	BDI, MFQ	28.8(7.9), 35.2 (9.4); 31.6 (10), 36 (10.7)	12	Published	Swedish Central Bank; Queen Silvia's Jubilee Fund, Sweden-America Foundation; Swedish Society of Medicine; Swedish Psychotherapy Society (Sweden)
Topooco (2019)	Placebo (supported); Guided (interactive)	37; 33	BDI > 14	17 (15–19)		Sweden (English)	Community	8-weekly sessions; 8 modules completed in own time and 8-weekly therapy sessions	BDI	32.3 (10.2); 33.1 (9.4)		Published	Queen Silvia's Jubilee Fund; Swedish Central Bank (Sweden)
Vostanis (1996)	Placebo (supported); Individual	28; 29	MFQ > 16	12.7 (8–17)	Depressed per DSM-III-R	UK (English)	Primary Care	9 fortnightly sessions spread over a maximum period of 6 months; 9 fortnightly session spread over a maximum period of 6 months	MFQ	28.6 (14.4); 33.4 (12.2)	9	Published	Merck Research Fund; Queen Elizabeth Psychiatric Hospital Trustees' Fund (UK)
Vuthiarpa (2012)a	TAU; Group	37; 37	CES-D >16, <24	15.5 (15–16)		Thailand (English)	School	NR; 12-weekly 1-h sessions	CES-D	19.74 (2.52); 19.66 (2.57)		Published	King Prajadhipok and Queen Rambhai Barni Memorial Foundation (Thailand)
Wijnhoven (2014)	None; Group	52; 50	CDI > 16	13.3 (11–15)		The Netherlands (English)	School	N/A; 8-weekly 50-min sessions	CDI, CES-D	19.31 (6.74), 24.68 (11.07); 15.82 (6.62), 19.53 (9.8)	6	Published	GGz Oost-Brabant; The Olim Foundation (Netherlands)
Woods (2011)	TAU; Group	12; 12	CDI > 63	14 (NR)		New Zealand (English)	School	NR; 8-weekly 90-min sessions	CDI	26.17 (4.32); 22.92 (6.63)	12	Published	Not reported
Wright (2019)	Placebo (self-help); Unguided (interactive)	69; 70	MFQ > 20	15 (12–18)		UK (English)	Clinical	Weekly sessions, flexible for the participant; Weekly sessions, flexible for the participant	BDI, MFQ	16, 35.3 (6.6, 9.9); 18, 37.5 (6.9, 9.2)	12	Published	National Institute for Health Research (UK)
Yu (2000)	None; Group	116; 104	CDI (top 25%) FES (top 25%)	11.8 (9–14)		China (English)	School	N/A; 10-weekly 2-h sessions	CES-D	16.72 (9.29); 17.44 (9.47)		Unpublished	Not reported – PhD

Abbreviations: BDI, Beck's Depression Inventory; CBT, cognitive behavioural therapy; CESD/CES-D, Centre for Epidemiologic Studies Depression Scale; CES-DC, CESD for Children; CESD-R, CESD Revised; CDI, Children's Depression Inventory; CDRS-R, Children's Depression Rating Scale-Revised; FES, Family Environment Scale; DSM, Diagnostic and Statistical Manual of Mental Disorders; Group, group CBT; Guided, guided self-help; HRSD, Hamilton Rating Scale for Depression; Individual, individual CBT; K-SADS, Children's Schedule for Affective Disorders and Schizophrenia; MASQ, Mood and Anxiety Symptom Questionnaire; MDD, major depressive disorder; MFQ, Mood and Feelings Questionnaire; N/a, not applicable; NR, not reported; PHQ:−9 Patient Health Questionnaire; RADS/RCDS, Reynolds Adolescent/Child Depression Scale; Remote, remotely-delivered CBT; QIDS-A-SR, Quick Inventory of Depressive Symptomatology – Adolescent Version; SD, standard deviation; SDS, Zung Self-Rating Depression Scale; SMFQ, Short MFQ; TAU, treatment-as-usual; Unguided, unguided self-help.

Cluster-randomised controlled trial. All other studies are parallel group, individually-randomised controlled trials.

Design

Eight included studies were cluster randomised trials (Bella-Awusah, 2016; Idsoe, 2019; Kerfoot, 2004; Kobak, 2015; Sheffield, 2006; Srivastava, 2015; Stallard, 2012; Vuthiarpa, 2012). The remaining 60 studies were parallel-group individually randomised controlled trials. There were 14 multi-arm studies, although more than two arms were included in the analysis for only seven studies (other multi-arm studies were Brent, 1997; Clarke, 1999; Hamamci, 2006; Kahn, 1988; Lewinsohn, 1990; Parks, 2013; Rossello, 1999; and Sheffield, 2006).

Sample size

The sample size ranged from 5 to 229 per node. Cluster trials had as many as 392 participants in one node.

Study setting

Studies were mostly conducted in schools (28) or universities (6). Other settings included clinical settings (9), primary care (13), community (3), home (2), education counselling centre (1) and penal settings (3). Three studies did not report the settings.

Trials were conducted across 21 different countries. The most common countries were USA (29), New Zealand (5), UK (4), Canada (3), Iran (3) and Thailand (3). Two studies each were conducted in China, India, Malaysia, Nigeria, the Netherlands, and Sweden. There were single studies from Australia, Belgium, Chile, Hong Kong, Japan, Norway, Puerto Rico, Spain and Turkey. Most included studies were written in English, except for one written in French (Marcotte, 1993) and one written in Persian (Rajabi, 2018).

Participants

The mean age of participants ranged from 10 to 19.5 years. 12 studies had a mean age of participants between 10 and 13, 32 between 14 and 15 and 19 between 16 and 19 years. Five studies did not report the mean age. The distribution of mean age across trials by pairwise comparison of nodes is presented in Figure 3.

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Figure 3

Boxplot of the distribution of mean age in individual trials across comparisons.

The proportion of females ranged from 7% to 100%. 17 studies had less than 50% females, 16 studies had 70% or more females. On average, 60% of participants were female. Four studies did not report participant gender.

Studies assessed inclusion using a range of different tools. Most commonly, participants were assessed using the Beck Depression Inventory (BDI) or the Child Depression Inventory (CDI). Thirteen studies did not assess participants for inclusion using a measure of depression but were included in this review as the mean baseline scores met our criteria.

The cut-off for all scales used in the review are reported in Table 1.

Baseline severity was investigated by representing each trial's baseline score as a percent above the cut-off score for elevated depression symptoms relative to the scale's maximum possible score and evaluating within and across comparisons. This value is similar to the percent of maximum possible value, except it reflects the observed score relative to the scale's cut-off rather than the minimum value (Cohen, 2010). Severity appeared to be heterogenous within some comparisons, but was not a clear threat to transitivity (Figure 4).

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Figure 4

Boxplot of pretest depression scores in individual trials across comparisons. The score from each trial is represented as a percent above the cut-off score for elevated depression symptoms relative to the scale's maximum possible score. For example, if a trial had a pretest score of 30 on the Beck Depression Inventory Second Edition (cut-off of 14 and maximum possible score of 63), this would translate to a value of (30 – 14)/(63 – 14) ∗ 100 = 33%. Note that some trials have a value below the cut-off (<0%) because they used multiple scales within the trial, and the scale prioritised for the review (based on frequency of scales used across all studies), may not have been the scale used to determine patient eligibility in the study.

Interventions

Amongst the 68 included studies, in terms of active treatment delivery models, 12 included therapist-delivered CBT in face-to-face individual sessions (individual CBT), 43 included therapist-delivered CBT in group sessions (group CBT) and one study included therapist-led CBT delivered remotely (remote CBT). The number of therapist-delivered sessions for these active interventions ranged from 4 to 16, the frequency of delivery from once every 2 weeks to twice a week and the duration of each session from 20 min to 2 h. Group sizes for group CBT ranged from 2 to 20, but were more commonly around 6 to 10. Thirteen studies evaluated unguided self-help and four studies evaluated self-help with therapist support (or guided self-help). The number of therapist-delivered sessions in the guided self-help models ranged from 1 to 8. The number of self-help modules across these two categories ranged from 4 to 12. The self-help interventions were further classified based on level of interactivity for the purposes of sensitivity analysis. Seven studies of unguided self-help and three studies of guided self-help were interactive, and six studies of unguided self-help and the self-help component of guided self-help in one study were not interactive.

Comparison interventions included no intervention/waitlist (30 studies; 25 waitlist, 5 no treatment), TAU (20) and placebo (21). Details about TAU were provided by 18 studies and were described as: freedom to continue pre-existing intervention or seek new assistance (4), self-help/written information (3), school nurse/counsellor (2), routine psychiatric interventions (1), therapy for depression (1), pharmacotherapy plus various therapy (1), counselling (1), vocational training (1), sessions with social worker (1), and various/self-selected (3). Placebos were classified as self-help (6), pill (1) and professionally supported (14). No systematic differences in dose of treatment were detected between interventions when delivered in trials with inactive control groups and trials with active controls.

There was 83% agreement between reviewers in initial node assignment (kappa 0.79 [95% CI: 0.71 to 0.86]). Nodes from one study (Sheffield, 2006) were excluded from this analysis as the node assignment was decided through discussion. In five cases, the final node classification ended up being completely different from the reviewers' initial assignment after review and discussion. In one case, the reclassification involved active treatment (group CBT to guided self-help), while the remaining cases involved reclassifying control nodes to another control.

Outcomes

Two studies did not use self-reported measures of depression and were thus not included in the quantitative analysis of the primary outcome (Rohde, 2014a, 2014b). Additionally, four studies were excluded from the analysis because we did not have suitable data to calculate the mean difference on the primary outcome at post-intervention and were unable to obtain the required data from the authors. The first, Stikkelbroek (2020), assessed individual CBT vs TAU and reported improvements in both conditions over time but no significant differences between conditions in self-reported depressive symptoms at post-treatment or 6-month follow-up. Similarly, Kobak (2015) compared individual CBT with TAU and found a reduction in depression in both groups and no significant difference in outcomes between trial arms. Lamb (1998) compared school-based group CBT with no treatment and also found reductions in depressive symptoms in both arms, with no significant differences between arms. Finally, Briere (2019) compared group CBT and an educational brochure in secondary schools and found significant differences, with greater reduction in symptoms of depression in group CBT compared to control at post-treatment, but no significant differences between arms at 6-month follow-up.

Of the 62 studies included in the quantitative analysis for the primary outcome at post-intervention, the most common measure was the Center for Epidemiologic Studies Depression Scale (CES-D). Other measures used and included in this review are BDI, CDI, Mood and Feelings Questionnaire (MFQ), and Reynolds Adolescent Depression Scale (RADS). One study each used the Short MFQ, Patient Health Questionnaire (PHQ-9), Zung Self-Rating Depression Scale (SDS), and Mood and Anxiety Symptom Questionnaire (MASQ). For all measures, a lower score indicates a more beneficial outcome; no reversal of scale direction was necessary for combining data.

Just under a third of studies (19) followed-up participants between six and twelve months after post-intervention assessments.

62 studies were included in the secondary analysis of the measure attrition as a proxy for acceptability.

Risk of bias in included studies

Figure 5 shows the overall risk of bias across studies by the different domains. Figure 6 lists the risk of bias individually for each study. These were created using https://mcguinlu.shinyapps.io/robvis/.

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Figure 5

Overall risk of bias across studies.

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The risk of bias was low across all domains for 23 studies. 24 studies had some concerns and the remaining 21 were assessed to be at high risk of bias.

Publication bias

Publication bias is suspected amongst studies comparing active and inactive control treatments. The comparison-adjusted funnel plot suggests that smaller studies tended to estimate greater improvements in post-treatment depression score from active treatments than larger studies do, with the Egger's test for small-study effects being statistically significant (p < 0.001) (Figure 7).

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Figure 7

Comparison-adjusted funnel plot of active versus inactive comparisons for post-test depression score. A prediction line representing the linear regression of the effect size standard error on the adjusted effect size is included. Egger's test for small-study effects is statistically significant (p < 0.001).

Effects of interventions

Network meta-analysis of cognitive behavioural therapy approaches

Primary outcomes

Depressive symptoms final score at post-intervention

Sixty-two RCTs (representing 6435 participants) were included in the pairwise and network meta-analyses for post-intervention depressive symptom score. Figure 8 presents a network plot showing how treatments were compared across the included RCTs. All pre-specified treatment and control categories were represented by at least one RCT. The number of RCTs comparing two interventions ranged between 1 and 24. Group CBT was the most commonly evaluated active condition and no intervention was the most commonly used control comparator. The network geometry indicates that guided self-help has not been directly evaluated against another active treatment and rCBT has only been compared to individual CBT.

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Figure 8

Network plot for post-test depression score. Nodes are weighted by the number of patients randomised to that intervention, and edges are weighted by the number of trials comparing the two interventions.

Of the seven cluster-randomised trials included in the analysis, two (Idsoe, 2019; Stallard, 2012) reported ICCs derived from the analysis (range of 0.025 to 0.099), and these values were used to adjust the standard error. One (Kerfoot, 2004) reported that it assumed an ICC of 0.3 in its sample size calculation, and we used this value for adjustment. The remaining trials did not report ICCs, and because of a generally similar setting, we imputed the value reported in Stallard (2012) (0.025) for the adjustment.

All active interventions except for remote CBT demonstrated superiority compared to no intervention, with the effectiveness ranging from an SMD of −1.29 (95% CI: −2.26 to −0.32) for guided self-help to −0.71 (95% CI: −1.30 to −0.12) for unguided self-help (Figure 9, Table 3). Fewer demonstrated superiority compared to TAU, and none to the placebo condition. In terms of comparative effectiveness, no active treatment demonstrated superiority over another, with the certainty of evidence ranging from low to very low. The highest and lowest ranking interventions were guided self-help (SUCRA 83%) and unguided self-help (SUCRA 51%), respectively (very low certainty in treatment ranking) (Figure 10, Table 3). Pairwise meta-analytic findings were generally similar to those of the network meta-analysis (Figure 11).

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Figure 9

Forest plot of posttest depression score network estimates comparing interventions and other controls with no intervention.

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Table 3

League table for post-test depression score.

Guided	-	-	-	-	-	-	-
0.17 (−1.92, 2.26)	Remote	-	−0.54 (−1.29, 0.22)	-	-	-	-
−0.38 (−1.33, 0.56)	−0.55 (−2.48, 1.38)	Group	-	−0.32 (−0.57, −0.06)	−0.49 (−0.87, −0.11)	−0.38 (−0.51, −0.24)	−0.87 (−1.23, −0.51)
−0.37 (−1.41, 0.68)	−0.54 (−2.35, 1.28)	0.02 (−0.65, 0.68)	Individual	-	−0.04 (−0.26, 0.18)	−0.91 (−2.02, 0.20)	−1.19 (−2.82, 0.44)
−0.58 (−1.58, 0.43)	−0.75 (−2.72, 1.22)	−0.20 (−0.77, 0.38)	−0.21 (−0.98, 0.56)	Unguided	−0.14 (−0.28, 0.01)	−0.29 (−0.60, 0.01)	−0.68 (−1.00, −0.37)
−0.80 (−1.67, 0.07)	−0.97 (−2.89, 0.95)	−0.42 (−0.89, 0.05)	−0.44 (−1.07, 0.20)	−0.22 (−0.79, 0.34)	Placebo	−0.20 (−0.50, 0.10)	-
−0.97 (−1.93, −0.01)	−1.14 (−3.07, 0.79)	−0.59 (−1.06, −0.11)	−0.60 (−1.28, 0.07)	−0.39 (−1.03, 0.25)	−0.17 (−0.74, 0.40)	TAU	-
−1.29 (−2.26, −0.32)	−1.46 (−3.39, 0.48)	−0.90 (−1.24, −0.56)	−0.92 (−1.60, −0.24)	−0.71 (−1.30, −0.12)	−0.48 (−1.00, 0.03)	−0.32 (−0.86, 0.23)	None
SUCRA
82.6%	76.9%	67.1%	66.0%	50.9%	31.9%	21.0%	3.5%

Note: Standardised mean differences (95% confidence intervals) for each comparison in the analysis of post-test depression score. Estimates below the diagonal represent network meta-analysis results while those above represent pairwise meta-analysis results. Below the diagonal, standardised mean difference <  0 favours the intervention in the column (above the diagonal, <0 favours the intervention in the row). Values are underlined when one intervention demonstrated superiority based on the confidence interval. Interventions are ordered based on the SUCRA values.

Abbreviations: CBT, cognitive behavioural therapy; Group, group CBT; Guided, guided self-help; Individual, individual CBT; Remote, remotely-delivered CBT; SUCRA, surface under the cumulative ranking area curve; TAU, treatment-as-usual; Unguided, unguided self-help.

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Figure 10

Cumulative ranking probabilities for each intervention in the post-test depression score network. Rank indicates the cumulative probability of the intervention being the best method, the second best, the third best, and so forth.

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Figure 11

Forest plot of direct estimates of comparative effectiveness of interventions, with corresponding indirect and network estimates, for post-test depression score. Intervention 1 is the treatment listed to the left in the treatment comparison column, and Intervention 2 is the treatment on the right. Sample size (number of randomised controlled trials and patients) and heterogeneity measures (I ² and τ ²) are provided for the direct estimates.

Based on χ ² and I ² statistics, heterogeneity within pairwise comparisons ranged from not important to considerable (Figure 11). At the network meta-analytic level, the extent of heterogeneity appeared to be moderate (τ ² = 0.71) compared to the empirical distribution for non-pharmacological interventions with mental health outcomes measured on a continuous scale (median τ ² = 0.058, 95% range = 0.001 to 2.58) (Rhodes, 2015). The loop-specific approach showed incoherence for the guided self-help, placebo, and TAU closed loop of evidence (incoherence factor [IF] = 0.803, 95% CI: 0.05 to 1.56, p = 0.037). The source of incoherence in this loop appears to be Saranya 2017, which is the only study comparing guided self-help and TAU, was conducted in an incarcerated population, and found a fairly large effect size for the treatment. While the node-splitting approach did not demonstrate clear incoherence (incoherence p-values ranged from 0.209 to 1.000), the direct and indirect estimates were notably different for individual CBT versus placebo, with the direct estimate suggesting no important difference between the groups (SMD −0.04, 95% CI: −0.26 to 0.18) and the indirect estimate indicating there may be an important difference(SMD −0.85, 95% CI: −1.79 to 0.10). The design-by-treatment interaction model did not detect incoherence (p = 0.973).

Depressive symptoms final score at 6 to 12 months follow-up

Nineteen RCTs (representing 3260 participants) were included in the pairwise and network meta-analyses for 6 to 12 months follow-up depressive symptom score.

Figure 12 presents a network plot showing how treatments were compared across the included RCTs. Neither guided self-help nor remote CBT were evaluated in the RCTs for this time point. The number of RCTs comparing two interventions ranged between 1 and 7. Group CBT was the most commonly evaluated active condition and placebo was the most commonly used control comparator. The network geometry indicates that individual CBT has not been directly evaluated against another active treatment.

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Figure 12

Network plot for 6- to 12-month follow-up depression score. Nodes are weighted by the number of patients randomised to that intervention, and edges are weighted by the number of trials comparing the two interventions.

The magnitude of effects appeared to be generally attenuated for 6- to 12-month outcomes compared to posttest. No interventions demonstrated superiority to no intervention (Figure 13), although unguided self-help (SMD −0.39, 95% CI: −0.75 to −0.03) and group CBT (−0.29, 95% CI: −0.51 to −0.07) both demonstrated superiority compared to TAU (Table 4). No active treatment demonstrated superiority over another. The highest and lowest ranking interventions were unguided self-help (SUCRA 84%) and individual CBT (SUCRA 35%), respectively (Figure 14, Table 4). Pairwise meta-analytic findings were similar to those of the network meta-analysis (Figure 15).

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Figure 13

Forest plot of 6- to 12-month follow-up depression score network estimates comparing interventions and other controls with no intervention.

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Table 4

League table for 6- to 12-month follow-up depression scores.

Unguided	−0.04 (−0.28, 0.19)	−0.19 (−0.50, 0.13)	-	−0.49 (−0.87, −0.11)	−0.18 (−0.49, 0.12)
−0.07 (−0.39, 0.24)	Placebo	−0.05 (−0.08, 0.17)	0.03 (−0.49, 0.56)	0.15 (−0.36, 0.66)	−0.24 (−0.54, 0.06)
−0.10 (−0.42, 0.22)	−0.03 (−0.25, 0.19)	Group	-	−0.25 (−0.59, 0.08)	−0.33 (−0.57, −0.08)
−0.29 (−0.82, 0.24)	−0.22 (−0.68, 0.24)	−0.19 (−0.65, 0.27)	Individual	-	0.01 (−0.26, 0.28)
−0.31 (−0.66, 0.03)	−0.24 (−0.51, 0.02)	−0.22 (−0.45, 0.02)	−0.02 (−0.52, 0.48)	None	-
−0.39 (−0.75, −0.03)	−0.32 (−0.60, −0.03)	−0.29 (−0.51, −0.07)	−0.10 (−0.54, 0.34)	−0.07 (−0.38, 0.23)	TAU
SUCRA
83.6%	73.8%	68.9%	34.8%	25.0%	13.9%

Note: Standardised mean differences (95% confidence intervals) for each comparison in the analysis of 6 to 12 month-follow-up depression score. Estimates below the diagonal represent network meta-analysis results while those above represent pairwise meta-analysis results. Below the diagonal, standardised mean difference  < 0 favours the intervention in the column (above the diagonal, < 0 favours the intervention in the row). Values are underlined when one intervention demonstrated superiority based on the confidence interval. Interventions are ordered based on the SUCRA values.

Abbreviations: CBT, cognitive behavioural therapy; Group, group CBT; Individual, individual CBT; SUCRA, surface under the cumulative ranking area curve; TAU, treatment-as-usual; Unguided, unguided self-help.

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Figure 14

Cumulative ranking probabilities for each intervention in the 6- to 12-month follow-up depression score network. Rank indicates the cumulative probability of the intervention being the best method, the second best, the third best, and so forth.

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Figure 15

Forest plot of direct estimates of comparative effectiveness of interventions, with corresponding indirect and network estimates, for 6- to 12-month follow-up depression score. Intervention 1 is the treatment listed to the left in the treatment comparison column, and Intervention 2 is the treatment on the right. Sample size (number of randomised controlled trials and patients) and heterogeneity measures (I ² and τ ²) are provided for the direct estimates.

Based on χ ² and I ² statistics, heterogeneity within pairwise comparisons ranged from not important to substantial (Figure 15). At the network meta-analytic level, the extent of heterogeneity appeared to be small (τ ² = 0.06) based on the empirical distribution for non-pharmacological interventions with mental health outcomes measured on a continuous scale (median τ ² = 0.058, 95% range = 0.001 to 2.58) (Rhodes, 2015). The loop-specific (IF p-values ranged from 0.228 to 0.944), node-splitting (incoherence p-values ranged from 0.186 to 0.759), and design-by-treatment interaction model (p = 0.979) approaches did not detect any incoherence.

Secondary outcomes

Acceptability of intervention

Sixty-two RCTs (representing 7347 participants) were included in the pairwise and network meta-analyses for intervention acceptability as measured by study attrition. Across these 62 studies, attrition rate was on average 11.2% at posttest. These 62 studies involved 130 intervention/control arms that can be classified as one of the nodes in this review. Attrition rate was calculated for each node and is reported in Table 5. Dropout from treatment was reported in only 13 studies. There was no dropout in one study, less than 5% in six studies, between 5% and 10% in 2 studies, and greater than 10% in the remaining 4 studies.

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Table 5

Attrition by node.

Node	Average completion	Data from number of trial arms
No intervention	92.6%	27/30
Therapist-delivered CBT – Group	89.4%	37/44
Placebo	88.6%	19/21
TAU	87.4%	18/21
Guided self-help	87.4%	4/4
Unguided self-help	87.1%	12/13
Individual CBT	84.3%	12/12
Remotely-delivered CBT	70.0%	1/1
Across nodes	88.8%	130/146

Figure 16 presents a network plot showing how treatments were compared across the included RCTs. All pre-specified treatment and control categories were represented by at least one RCT. The number of RCTs comparing two interventions ranged between 1 and 22. Group CBT was the most commonly evaluated active condition and no intervention was the most commonly used control comparator. The network geometry indicates that guided self-help has not been directly evaluated against another active treatment and remote CBT has only been compared to individual CBT.

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Figure 16

Network plot for intervention acceptability. Nodes are weighted by the number of patients randomised to that intervention, and edges are weighted by the number of trials comparing the two interventions.

Although point estimates tended to favour no intervention, no active treatments were clearly inferior, with estimates ranging from an OR of 1.45 (95% CI: 0.31 to 6.85) for remote CBT to 0.97 (95% CI: 0.58 to 1.60) for individual CBT (Figure 17, Table 6). Findings were similar with TAU or placebo as the comparator. No active treatment demonstrated superiority over another. The highest and lowest ranking active interventions were individual CBT (SUCRA 60%) and group CBT (SUCRA 21%), respectively (Figure 18, Table 6). Pairwise meta-analytic findings were similar to those of the network meta-analysis (Figure 19).

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Figure 17

Forest plot of intervention acceptability network estimates comparing interventions and other controls with no intervention.

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Table 6

League table for intervention acceptability.

Placebo	0.86 (0.49, 1.5)	2.93 (0.3, 28.74)	0.96 (0.46, 2)	0.72 (0.4, 1.3)	0.45 (0.12, 1.74)	-	0.66 (0.42, 1.03)
0.85 (0.55, 1.29)	Individual	1.05 (0.63, 1.75)	0.71 (0.18, 2.79)	-	-	0.67 (0.15, 2.89)	-
0.84 (0.56, 1.25)	0.99 (0.66, 1.50)	TAU	-	1.04 (0.54, 1.99)	1 (0.02, 51.57)	-	0.94 (0.51, 1.74)
0.82 (0.54, 1.23)	0.97 (0.58, 1.60)	0.98 (0.63, 1.51)	None	1.81 (0.47, 6.98)	-	-	0.75 (0.57, 1.01)
0.75 (0.53, 1.08)	0.89 (0.53, 1.48)	0.90 (0.57, 1.41)	0.92 (0.58, 1.47)	Unguided	-	-	1.39 (0.52, 3.7)
0.72 (0.36, 1.45)	0.86 (0.38, 1.93)	0.86 (0.39, 1.91)	0.89 (0.39, 2.02)	0.96 (0.43, 2.14)	Guided	-	-
0.56 (0.12, 2.60)	0.67 (0.15, 2.90)	0.67 (0.15, 3.10)	0.69 (0.15, 3.26)	0.75 (0.16, 3.55)	0.78 (0.15, 4.17)	Remote	-
0.65 (0.45, 0.94)	0.77 (0.48, 1.22)	0.77 (0.54, 1.11)	0.79 (0.60, 1.05)	0.86 (0.56, 1.32)	0.89 (0.40, 2.00)	1.15 (0.25, 5.36)	Group
SUCRA
84.8%	59.7%	59.6%	56.7%	42.9%	42.3%	32.6%	21.3%

Note: Odds ratios (95% confidence intervals) for each comparison in the analysis of intervention acceptability. Estimates below the diagonal represent network meta-analysis results while those above represent pairwise meta-analysis results. Below the diagonal, odds ratio < 1 favours the intervention in the column (above the diagonal, <1 favours the intervention in the row). Values are underlined when one intervention demonstrated superiority based on the confidence interval. Interventions are ordered based on the SUCRA values.

Abbreviations: CBT, cognitive behavioural therapy; Group, group CBT; Guided, guided self-help; Individual, individual CBT; Remote, remote CBT; SUCRA, surface under the cumulative ranking area curve; TAU, treatment-as-usual; Unguided, unguided self-help.

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Figure 18

Cumulative ranking probabilities for each intervention in the intervention acceptability network. Rank indicates the cumulative probability of the intervention being the best method, the second best, the third best, and so forth.

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Figure 19

Forest plot of direct estimates of comparative effectiveness of interventions, with corresponding indirect and network estimates, for intervention acceptability. Intervention 1 is the treatment listed to the left in the treatment comparison column, and Intervention 2 is the treatment on the right. Sample size (number of randomised controlled trials and patients) and heterogeneity measures (I ² and τ ²) are provided for the direct estimates.

Based on χ ² and I ² statistics, heterogeneity within pairwise comparisons ranged from not important to considerable (Figure 19). At the network meta-analytic level, the extent of heterogeneity appeared to be minimal (τ ² ≈ 0) based on the empirical distribution for non-pharmacological interventions with semi-objective outcomes measured by OR (median τ ² = 0.056, 95% range = 0.001 to 2.35) (Turner 2012). The loop-specific (IF p-values ranged from 0.486 to 0.875), node-splitting (incoherence p-values ranged from 0.255 to 0.999), and design-by-treatment interaction model (p = 0.801) approaches did not detect any incoherence.

Subgroup and sensitivity analyses

Depressive symptoms final score at post-intervention

Subgroups by age category

Fifty-seven of the 62 trials included in the overall analysis for post-test depression score reported participant mean age. The mean age of participants was between 10 and 13 for 12 RCTs, between 14 and 15 for 28 RCTs, and between 16 and 19 for 17 RCTs (Figure 20). Group CBT was the most commonly studied intervention for all subgroups. Guided self-help was only evaluated amongst RCTs focusing on participants in the oldest age category, while remote CBT was only evaluated in an RCT focusing on participants in the youngest category.

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Figure 20

Network plot for post-test depression score by age category subgroups. Nodes are weighted by the number of patients randomised to that intervention, and edges are weighted by the number of trials comparing the two interventions. Additionally, the subgroup networks are scaled based on the proportion of data they represent from the overall network.

There may be subgroup effects by age category. Using the no intervention control group as the reference, the magnitudes of effects appear to be larger for the oldest age categories compared to the other subgroups for each given comparison. However, they were also generally less precise and formal testing only indicated a significant difference for group CBT (Figure 21).

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Figure 21

Forest plot of the network estimates for post-test depression score for each intervention compared to no intervention by age category. p Values and I ² values for subgroup differences are included.

Sensitivity analyses

Our findings were generally robust to pre-specified sensitivity analyses separating out the type of placebo and excluding cluster-RCTs, as well as an additional analysis excluding studies where we had imputed SDs (Table 7). In the pre-specified analysis excluding studies allowing for interactivity of the intervention, the effect for guided self-help, the highest-ranking intervention in the primary analysis, was notably attenuated (primary analysis SMD vs. no intervention: −1.29; sensitivity analysis SMD vs. no intervention: −0.77). We were not able to conduct the analyses evaluating the effects of intervention components due to lack of reported information in the studies, nor were we able to exclude studies using unvalidated measures due to all studies using validated measures.

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Table 7

Sensitivity analysis results for post-test depression score.

Versus None	Primary analysis (62 trials, n = 6436)	Separate placebo types (62 trials, n = 6436)	Excluding interactive interventions (52 trials, n = 5470)	Excluding cluster trials (55 trials, n = 4768)	Excluding imputed SDs (59 trials, n = 6321)
Guided	−1.29 (−2.26, −0.32)	−1.28 (−2.27, −0.29)	−0.77 (−2.68, 1.13)	−1.45 (−2.44, −0.46)	−1.40 (−2.35, −0.44)
Remote	−1.46 (−3.39, 0.48)	−1.53 (−3.50, 0.43)	−1.47 (−3.53, 0.59)	−1.65 (−3.60, 0.29)	−1.53 (−3.42, 0.37)
Group	−0.90 (−1.24, −0.56)	−0.90 (−1.25, −0.56)	−0.90 (−1.26, −0.54)	−0.95 (−1.31, −0.58)	−0.90 (−1.24, −0.55)
Individual	−0.92 (−1.60, −0.24)	−0.99 (−1.71, −0.28)	−0.93 (−1.66, −0.20)	−1.12 (−1.84, −0.40)	−0.99 (−1.66, −0.32)
Unguided	−0.71 (−1.30, −0.12)	−0.72 (−1.37, −0.07)	−0.68 (−1.54, 0.18)	−0.81 (−1.41, −0.21)	−0.79 (−1.40, −0.18)
Placebo	−0.48 (−1.00, 0.03)	-	−0.45 (−1.03, 0.13)	−0.70 (−1.26, −0.14)	−0.62 (−1.14, −0.10)
Pill placebo	-	−1.09 (−2.93, 0.74)	-	-	-
Self-help placebo	-	−0.55 (−1.45, 0.35)	-	-	-
Therapist-led placebo	-	−0.47 (−1.03, 0.09)	-	-	-
TAU	−0.32 (−0.86, 0.23)	−0.33 (−0.88, 0.23)	−0.39 (−1.01, 0.23)	−0.35 (−0.95, 0.25)	−0.35 (−0.90, 0.19)

Note: Values represent standardised mean differences (95% confidence intervals).

Abbreviations: CBT, cognitive behavioural therapy; Group, group CBT; Guided, guided self-help; Individual, individual CBT; Remote, remotely-delivered CBT; SD, standard deviation; TAU, treatment-as-usual; Unguided, unguided self-help.

Summary of main results

Sixty-two studies were included in the network meta-analysis for the primary outcome of depression symptoms at posttreatment, and each of the pre-specified treatment and comparison nodes was represented as a trial arm by at least one study. At posttreatment, all active treatments (guided self-help, group CBT, individual CBT, and unguided self-help) except for remote CBT were found to be more effective than no treatment. However, only guided self-help and group CBT were found to be more effective than TAU. Guided self-help was the most highly ranked intervention, but the subgroup analysis revealed that it was only evaluated in trials with the oldest adolescents (ages 16–19 years). The results for remotely-delivered CBT should be treated with caution as it was only evaluated in one included study with the youngest adolescents (10–13 years). The magnitude of effects also appeared to be greatest in the older age categories for each comparison, where these age groups were included in studies. However, this needs to be interpreted with caution due to the possibility of ecological bias.

The standardised effects at posttreatment are presented in terms of the difference in points on the BDI-II between active interventions in the Summary of findings Table 1. These scores ranged from mean differences of 6.8 points to 0.2 points between intervention delivery formats. For context, the minimum clinically important difference in scores on the BDI-II is likely to fall in the range of 3–6 points, with average treatment effects of antidepressants being 2 points (Hengartner, 2021).

Nineteen studies reported data for depressive symptom outcomes at 6-12 month follow up. None of the included studies evaluating guided self-help or remote CBT reported outcomes at this time point. The magnitude of effects appeared to be generally attenuated for 6- to 12-month outcomes compared to post-intervention. Although unguided self-help was the lowest-ranked active intervention at post-intervention, it was the most highly ranked at 6 to 12-month follow-up.

In the analysis of treatment acceptability, 62 studies were included, with at least one study representing each of the pre-specified active and control nodes in the network. We did not find clear evidence that any of the active treatments were more acceptable to participants than any others, based on attrition. This is in line with a review which found that drop-out rates for computerised CBT for depression was similar to drop-out rates for other psychological therapies including face-to-face CBT (Kaltenthaler, 2008), as well as another review which found no significant differences in acceptability between delivery formats of CBT for adults with depression (Cuijpers, 2019). In addition, a recent rapid review of the evidence found that engagement was lower and drop-out was higher when adolescents were randomised to mental health treatment delivery formats, with drop-out being much lower when young people could choose how to access support, indicating that randomised trials may not be the optimum design for assessing acceptability of different delivery formats (James, 2020).

Overall completeness and applicability of evidence

Only one study examining remote delivery of CBT for younger adolescents with depression was retrieved in the search, limiting the conclusions that may be drawn about the relative effectiveness of this particular mode of delivery and its effectiveness for older adolescents. In addition, all studies evaluating guided self-help included older adolescents. These results may therefore only be applicable to this age group and research is needed to assess the effectiveness and acceptability of guided self-help for younger adolescents with depression.

Very few studies included a follow-up assessment 6 to 12 months after the end of the intervention. Although this is a common problem in trials of interventions, it is important that future studies follow young people up over longer periods to determine whether the effects of different delivery models of CBT are maintained.

Studies conducted in the United States were overrepresented (n = 29), potentially affecting the generalisability of the findings. However, this is not a major concern as studies from 21 different countries were included, representing a range of contexts. We were unable to find some papers (n = 39) or obtain the required information for others (Studies awaiting classification, n = 5) and thus these were excluded from the review, despite our attempts to contact authors.

We excluded studies in which the intervention was focused on treating comorbid conditions, which may be atypical for the population seen by services (Essau, 2009; Rao, 2009).

Quality of the evidence

Overall, our confidence in the evidence for post-test depression symptoms was low or very low. Reasons for downgrading the evidence include a high prevalence of studies at unclear or high risk of bias in the network, the inclusion of some moderately indirect studies, imprecise effect estimates, and heterogeneity between the studies within some comparisons. Although heterogeneity appears to be moderate to large for a few comparisons, most of the comparisons have a fairly small evidence base. These cases preclude reliably estimating heterogeneity statistics as well as thoroughly investigating how sources of heterogeneity may differ between comparisons and affect transitivity. Three studies (Fischer, 1996; Rohde, 2004; Saranya, 2017) were considered to be indirect due to using incarcerated adolescent populations, three (Araki, 2019; Topooco, 2017, 2019) due to transitivity concerns with the comparison they assessed (guided self-help vs. Placebo) only focusing on older adolescents, and one study (Nelson, 2003) due to transitivity concerns with it being the sole representative for a direct comparison (individual CBT and remote CBT).

Potential biases in the review process

The assignment of trial arms to network nodes has a degree of subjectivity and the authors did not always agree on node assignments. Different teams of authors therefore may have come to different decisions about node assignments for this review, which could introduce a bias.

There was some indication of publication bias, which may mean that the effects of the active treatments are inflated when compared to inactive controls. However, it is not clear that this implies that the relative effectiveness between any of the active treatments is inflated.

It was not possible to find papers for 39 studies at the full text screening stage, which could have introduced a bias, although we were not able to determine from available information whether these studies would have met the inclusion criteria and have no reason to believe that they would necessarily have had results that differed from the findings of this review. Similarly, we were unable to include the data for five included studies in the network meta-analysis. These studies indicated no significant differences in depression outcomes for comparisons of group CBT vs unguided self-help and for individual CBT versus TAU. These results are not inconsistent with the findings of this review for these comparisons. For three included studies, the standard deviations of outcome measures were not included in the papers, and we were unable to obtain them by contacting authors, so these were imputed. However, we have no reason to expect that this introduced a bias in the results.

The secondary outcome is limited in that loss to follow-up is an imperfect proxy for treatment acceptability. In particular, completion of post-test measures may not have been entirely related to engagement with treatment, particularly if incentives and other methods were used to boost response rate. Similarly, where interventions were delivered in schools, attendance to take part in the intervention and for measure completion would have been compulsory regardless of whether students found the intervention acceptable. However, this proxy facilitated quantitative comparison between studies on a consistent measure.

Agreements and disagreements with other studies or reviews

In their systematic review comparing delivery formats of CBT for adult depression, Cuijpers (2019) found that there was no statistically significant difference in effectiveness between individual, group, telephone, or guided self-help formats and that all of these formats were more effective than unguided self-help as well as waiting list and care as usual control conditions. In contrast, in this review we found that all active treatments except for remote CBT were more effective than no treatment, and that the comparisons between active treatments demonstrated neither superiority nor equivalence.

López-López (2019) found the biggest effects for face-to-face CBT, with more uncertainty for the effectiveness of multimedia CBT or hybrid models of CBT, but found little evidence of differential effectiveness of face-to-face versus multimedia CBT interventions in a components analysis. Similarly, Bennett (2019) found significant effects for guided self-help and unguided self-help on symptoms of anxiety, depression, and disruptive behaviour when compared to controls, but negative effects when compared to face-to-face therapy, although they report that the difference in effect sizes between self-help and face-to-face therapy was small and unlikely to be clinically significant. The results of this review are more nuanced, in that both face-to-face and hybrid models were found to be more highly ranked than unguided self-help at posttreatment assessment time points, with no significant differences in effectiveness, and with unguided self-help ranking higher than face-to-face therapy at 6- to 12-month follow-up.

A systematic review of the acceptability to patients of computerised CBT for depression in adults found that drop-out rates were comparable to rates found for other forms of treatment in other studies (Kaltenthaler, 2008). Similarly, we found that none of the active treatment delivery models were relatively superior to any other in terms of attrition.

Implications for practice

The findings of this review have implications for policy and practice and the future funding of mental health service provision by providing an understanding of how different CBT delivery modes compare to one another on a subpopulation of adolescents with elevated symptoms of depression.

Although guided self-help had the highest ranking at post-intervention, the included studies vary in terms of the type and amount of therapist support provided. Three of the studies examining guided self-help involved online or app-based interventions (Saranya, 2017; Topooco, 2017, 2019), while the fourth involved reading and worksheets for the self-help element (Araki, 2019). Therapist support in these studies took the form of individual therapy delivered via chat (Topooco, 2017), individual face-to-face therapy sessions along with messages in the app (Topooco, 2019), a single group CBT session (Araki, 2019), or brief therapist feedback and reinforcement on homework each week (Saranya, 2017). The high ranking of unguided self-help in the longer term indicates that interventions with self-directed elements may provide young people with skills or resources that they can use to maintain the effects of the intervention, although this needs further investigation.

None of the active treatments were clearly more acceptable to participants than others, using drop-out rates as a proxy for treatment acceptability.

The results of the network meta-analysis may only apply to the oldest adolescents. In particular, effectiveness of guided self-help was only found in studies of 16–19 year olds; we did not find any studies of guided self-help with children under 16 years of age.

Finally, in clinical practice, the relative effectiveness of these intervention delivery modes must be taken into account in the context of the needs and preferences of individual young people, particularly as the differences between effect sizes were relatively small.

Implications for research

As guided self-help was not directly evaluated against any of the other active treatments in this review, the results are based on indirect evidence only. Given that guided self-help appeared to be the highest ranked intervention, at least in the short term, direct comparisons would provide further insight into not only the relative effectiveness of guided self-help compared to other delivery formats, but also acceptability and cost-effectiveness.

Further research into the type and amount of therapist support that is most acceptable to young people and most cost-effective would be particularly useful. Two recent scoping reviews found that involvement of young people in research to develop preventative digital mental health interventions for children and young people, or in child health research more generally, has not been frequently reported (Bergin, 2020; Sellars, 2021). Involvement of young people in future intervention development research may increase the acceptability of different modes of delivery and may increase the chances of developing effective interventions in different formats for a wider range of ages.

Remote delivery is particularly relevant in the context of the COVID-19 pandemic. However, this review was only able to include one study of remote delivery of CBT. Results from trials of this delivery format are needed to help commissioners and practitioners understand whether this is an effective alternative to face-to-face therapy.

Furthermore, trials evaluating guided self-help and remote CBT did not collect longer-term follow-up data. Results over the long term are needed to determine whether effects persist over time for CBT when delivered using these formats. The high ranking of unguided self-help at 6- to 12-month follow-up has important implications for further research into whether interventions with self-directed elements enable young people to maintain effects by continuing or revisiting the intervention independently, and whether therapist support would improve long-term outcomes.

Delivery modalities will differ in terms of demands on resources. This review may therefore have important cost–benefit implications, which could be examined in further research (Arnberg, 2014).