Abstract
Background:
Existing quantitative evidence suggests that at a population level, socioeconomic factors affect access to preferred place of death. However, the influence of individual and contextual socioeconomic factors on preferred place of death are less well understood.
Aim:
To systematically synthesise the existing qualitative evidence for socioeconomic factors affecting access to preferred place of death in the United Kingdom.
Design:
A thematic synthesis of qualitative research.
Data sources:
Cochrane Library, MEDLINE, Embase, CINAHL, ASSIA, Scopus and PsycINFO databases were searched from inception to May 2018.
Results:
A total of 13 articles, reporting on 12 studies, were included in the synthesis. Two overarching themes were identified: ‘Human factors’ representing support networks, interactions between people and decision-making and ‘Environmental factors’, which included issues around locations and resources. Few studies directly referenced socioeconomic deprivation. The main factor affecting access to preferred place of death was social support; people with fewer informal carers were less likely to die in their preferred location. Other key findings included fluidity around the concept of home and variability in preferred place of death itself, particularly in response to crises.
Conclusion:
There is limited UK-based qualitative research on socioeconomic factors affecting preferred place of death. Further qualitative research is needed to explore the barriers and facilitators of access to preferred place of death in socioeconomically deprived UK communities. In practice, there needs to be more widespread discussion and documentation of preferred place of death while also recognising these preferences may change as death nears or in times of crisis.
Socioeconomic factors affect palliative care provision, including access to preferred place of death.
Quantitative studies have demonstrated associations between place of death and social class, with people from higher socioeconomic groups more likely to die at home or in hospices, and less likely to die in hospital, than people from lower socioeconomic groups.
There is limited discussion of socioeconomic factors affecting preferred place of death in UK qualitative literature.
The main factor affecting access to preferred place of death was the presence of social support.
There was fluidity around the concept of ‘home’ and around the location of preferred place of death itself towards the end of life.
Further qualitative research is needed to explore the barriers and facilitators of access to preferred place of death in socioeconomically deprived UK communities.
In practice, there needs to be more emphasis on both discussing and documenting preferred place of death, which can be managed through existing care pathways.
Care plans should be reviewed appropriately in recognition that these preferences are liable to change as death nears or in times of crisis.
Introduction
Socioeconomic factors affect palliative care provision, including access to preferred place of death. UK-based quantitative studies have shown links between place of death and social class, with people from higher socioeconomic groups more likely to die at home or in hospices, and less likely to die in hospital, than people from lower socioeconomic groups.1–4 Similarly, in the United States, Howell et al. 5 found that higher earners were more likely to die at home, and a systematic review by Cohen 6 found that 12 out of 13 studies showed differences between minority ethnic groups and White Americans. Other international studies have associated low educational attainment with reduced access to specialist palliative care services.7,8
Preferred place of death is a key part of many national policies on end-of-life care. However, it is less visible in academic literature than actual place of death, for which quantitative data are much more widely available. Key socioeconomic determinants such as occupation, income, ethnicity and postcode are easier to measure quantitatively, both through targeted surveys and through routinely collected data. Direct correlations between socioeconomic status and place of death can therefore be measured on larger populations quantitatively; however, this does not allow for exploration of the nuances behind these associations.
Qualitative research can enhance the evidence from quantitative studies by highlighting individuals’ own perceptions of their care needs.9,10 Qualitative evidence synthesis is particularly relevant in palliative care as it maximises value from studies that have investigated difficult subject matter around end of life. 11 This study aims to contextualise qualitative data by synthesising the existing qualitative evidence for socioeconomic factors affecting access to preferred place of death in the United Kingdom.
Methods
Search strategy
A systematic approach to searching was undertaken to address the research question ‘what, and in what ways, do socioeconomic factors affect access to preferred place of death in the UK?’.
First, it was important to identify what terms to use to define ‘socioeconomic factors’. An iterative approach was taken due to the lack of a universally accepted definition of socioeconomic disadvantage. A series of initial searches were run using variations on definitions of ‘socioeconomic factors’ (e.g. relating strictly to social class and economics or including people more broadly at socioeconomic disadvantage, such as the homeless). As searching for strict socioeconomic terms did not identify articles more specifically related to socioeconomically disadvantaged populations, the decision was taken to include a broad set of socioeconomic terms, compiled after reviewing search terms from other articles with similar themes.12–17 These included terms covering social class, income, unemployment, ethnicity, homelessness, detainees, travelling communities, migrants/refugees, literacy/education levels and socially disadvantaged/excluded groups.
The search terms used in the final strategy covered three main areas: socioeconomic factors, place of death and palliative care or carers. Finally, a three-term qualitative filter was added (qualitative, finding* and interview*). 18 The full list of search terms is included as Appendix A of the Supplemental material.
Seven electronic databases containing relevant peer-reviewed journals were searched from inception until June 2016: Cochrane Library, MEDLINE, Embase, CINAHL, ASSIA, Scopus and PsycINFO. A further search (using identical terms but restricted to the last 2 years) was carried out in May 2018 to identify any further articles published since the initial search date.
Inclusion criteria
Articles were included if they satisfied the following criteria:
Discussed preferred place of death and at least one of the identified socioeconomic factors (as set out in the search strategy) in a population of UK residents;
Reported on data collected and analysed using qualitative methods (mixed methods articles were included if qualitative findings were reported separately);
Were written in English and published in an academic journal.
No date restrictions were included. Papers were restricted to a single health system (United Kingdom) due to concerns over the generalisability of economic factors affecting access to health care between health systems with different economic components. However, as some of the social factors faced are similar across nations with differing healthcare systems, the broader findings are still relevant to an international audience.
Quality appraisal
Quality appraisal was undertaken to provide a transparent assessment of the methodological strengths and limitations of included articles. This used a tool developed by Hawker et al., 19 which has been extensively used in systematic reviews of qualitative research and is also able to cover mixed methods (and quantitative) studies. The appraisal process was carried out by a single reviewer (V.T.), with a second reviewer (K.F.) checking a sample of forms for consistency. There was no a priori cut-off score for inclusion on the grounds of quality; however, it was important to consider any papers of very low quality when examining the reliability of the results.
Data extraction
Data extraction was completed in two phases. First, summary data and population details were extracted using a standardised extraction form. Second, the results/findings sections (including text and tables/diagrams) from each paper were copied into Microsoft Word. A decision was taken not to analyse the discussion section to minimise the risk of subjective bias from the original authors.
Data analysis
Findings were analysed using thematic synthesis, 20 a method used to bring together and integrate the findings of multiple qualitative studies. 21 Coding was carried out according to Thomas and Harden’s 20 approach to thematic synthesis by one reviewer (V.T.) and checked by a second (K.F.). First, the text was processed line by line and individual codes were identified. These were reviewed following repeat readings of the text to check for consistency. Once each article had been coded, the individual codes were organised into broader groups of similar codes to develop descriptive themes. These themes were then reviewed collectively by both authors to produce the final list of themes and subthemes. The derivation of themes was predominantly inductive, although there was a small deductive component as the process was guided by the overall research question. The order in which the papers were coded was not predetermined as papers were considered to all be of equal value. However, attempts were made not to code two similar papers (e.g. interviews with nursing home staff) in a row to prevent simply copying codes from one paper to the next.
The paper has been reported in accordance with the enhancing transparency in reporting the synthesis of qualitative research (ENTREQ) guidelines. 22
Results
A total of 2726 papers were identified during the initial search process. One reviewer (V.T.) removed duplicates and reviewed titles and abstracts to remove clearly irrelevant articles, leaving 142 articles remaining. This decreased to 26 following removal of non-UK results. Both reviewers then collectively reviewed the remaining papers, identifying 13 that fitted all the inclusion criteria.
The update search run in May 2018 identified 296 papers initially (268 once duplicates removed). Following screening, 11 articles were reviewed in full; however, none of these fulfilled all the inclusion criteria and so were not included in the review (Figure 1).

PRISMA flowchart of article selection.
In total, 13 articles, covering 12 studies, were included in the final review (see Appendix B of the Supplemental material), of which 10 were purely qualitative23–32 and 3 were mixed methods.33–35 Six had a primary population made up of staff members,23,24,27,30,31,34 two looked at informal carers/relatives,29,33 one looked at community groups representing older people 26 and four reviewed participants’ own feelings regarding end-of-life issues.25,28,32,35
Socioeconomic profile of participants
In terms of socioeconomic characteristics, the included papers were extremely heterogeneous. They were largely poor at discussing socioeconomic factors explicitly, and there was also poor reporting of the socioeconomic makeup of the participants. In total, six articles reported gender,23,25,26,28,32,34 five reported ethnicity,23,26,28,32,33 four reported age,25,26,28,32 four reported residence25,26,28,32 and two reported social class.29,32 None reported specifically on participants’ income or educational level.
Ethnicity
Where stated, the majority of the participants were described as White British, except in articles where ethnic minorities were explicitly studied (one looking at Chinese and one looking at Black Caribbean groups).
Age
Most were from older age groups, except articles that interviewed medical professionals and the gypsy/traveller community (mixed ages). Most papers reported age as ranges, with an overall age range of 15–20 years old to 80–90 years old.
Residence
Where residence was noted within papers it usually involved care homes, although participants in one study all lived in gypsy/traveller communities. Two articles stated when participants came from deprived geographic areas.
Social class
In the two papers where social class was specifically reported, both determined class using last known occupation.
Socioeconomic content of articles
Different socioeconomic factors were addressed in different papers (Table 1).
Socioeconomic content of articles.
Despite including specific search terms in these areas, no UK articles were found that discussed education level/literacy, homelessness or migrants/refugees.
Quality appraisal scores for the included articles were generally between 26 and 33 (overall range of 21–35), suggesting that most articles were of good quality. Lower scores were often due to poor reporting around bias, particularly around the position of the researcher.
Through the process of coding, developing codes into descriptive themes and then into analytical themes (an example of which is shown in Table 2), two overarching analytical themes were identified: ‘Human factors’ and ‘Environmental factors’. Human factors detail the interactions between individuals and their support networks and how these connections can facilitate or deny access to preferred place of death. Environmental factors explore the physical location of where care takes place, alongside the physical resources available (or required) within those environments. Each of these themes was sub-divided further as shown in Table 3. Themes include information on specific socioeconomic findings and also broader issues around accessing preferred place of death. Quotes presented below in ‘italics’ are from research participants; quotes in ‘regular font’ are from authors of the original papers.
Example of coding process.
Overview of themes and subthemes.
Human factors
While individuals generally stated their own preferred place of death, it was the people around them that had the most influence as to whether they were able to die there. There was little explicit discussion of socioeconomic factors, with the size of support networks and the skill set of carers as the most frequently discussed topics. Three main factors were influential: supporting networks, interactions between people and decision-making.
Support networks
Families were a key part of most support networks. The family background of the dying person plays a significant role in end-of-life care; socioeconomic and cultural factors were most evident here.
Evidence from the reviewed papers suggests that differences in social class did not seem to make much difference to the type of care individuals could access, with problems regarding access spread across all classes. This was seen explicitly in the two papers discussing social class29,32 and failed to arise as an issue in any of the other papers. The only suggestion that higher classes had any advantage was through being more willing to engage in more forceful negotiations, which sometimes (but not always) led to a change in care. In contrast, carers from lower socioeconomic classes had greater ability to draw on support from a second carer, as they had more family members living nearby.
29
However, trying to pinpoint the social class of a whole family using typical measures (i.e. social class based on their last known job) was difficult, with even small family groups presenting as a mix of classes. In terms of economic factors, lower classes were less concerned about finances and loss of earning potential than higher classes, despite having more poorly paid jobs:
29
Families often relied on their most forceful members, particularly children of higher social class, to help negotiate these barriers.
29
Contrasting attitudes to end-of-life care were seen among people of different ethnicities, with particular groups facing specific challenges. For example, gypsy traveller communities displayed high levels of resilience due to their unwillingness to rely on external services.
28
In another example, Chinese elders had ideas about dying in the home that were not shared by other cultures:
32
And if you die in the house, you know, the house is not a good house any more … no Chinese would buy a car that had been in an accident. (Chinese elder)
32
Regardless of the socioeconomic status, the size and composition of an individual’s support network had a significant effect on preferred place of death and the ability to die there. Absence of a support network, usually family, was the main barrier to dying at home. Four papers suggested that living alone meant it was not realistically possible to die at home.26,27,31,32 In other cases, the expertise of the carers affected whether patients could be cared for and die at home and the level of any extra support required. The ability of carers to cope generally deteriorated during the final phase of illness, leading to last-minute transfers. Patients’ concerns about carers’ ability to cope also influenced place of death, with individuals not wishing to become a burden on their family.26,27,30,32,35 Some individuals were also selective about who they wanted to care for them, which directly affected preferred place of death.26,28,32 In some communities (e.g. gypsy travellers or historically in UK culture), caring was a gender-specific role. For some people, the intimate nature of care led to embarrassment; while people were willing to accept partners as carers, they did not wish for wider family members to take on this role: Participants who did not have close relatives, especially those who were widowed or separated, felt that this meant they were automatically excluded from the possibility of being cared for at home.
26
Interactions between people
Individuals reported the importance of having people present when they died, which in turn affected their choice of preferred place of death.24,26,28,29,32–34 People wanted to die surrounded by people they knew, which could be family, care home staff or, in some cases, hospital staff.
26
Dying with anyone present, even if not closely known, was generally considered better than dying alone: George was initially excited about the prospect of release [from prison]; however, with no family or friends to support him on the outside he quickly found himself socially isolated and would have preferred to die in prison amongst people he knew.
34
However, poor communication often hampered accessing preferred place of death. Failure to talk about death was common; patients, carers and staff all found conversations hard to initiate, with some feeling it would not be in individual’s best interests (by causing distress and quashing hope).28,30,32,35
Communication with healthcare practitioners was also variable. Positive relationships required trust to enable productive discussion on preferred place of death. However, poor communication between healthcare practitioners and families, and between different groups of healthcare practitioners, hampered effective care and the achievement of patients’ wishes:
If there was a little bit more communication between the ward staff and us here in the community, I think we could overcome a lot of these problems. (District nurse)
31
Decision-making
The decision-making process was key to determining preferred place of death. This was often influenced by someone other than the patient, including family and healthcare practitioners. Fear was another strong influencer, with fears around becoming a burden and the prospect of worsening symptoms overriding existing views on preferred place of death. Changing decisions was a key theme in three papers.26,27,30 This was particularly common towards the end of life where symptoms worsened; preferred place of death changed to places where higher degrees of medical input could be provided. Some people also changed preference in order to remain in their current location, due to increased familiarity and comfort. Some people, particularly the very elderly in care homes or with dementia, felt they were not able to make end-of-life care decisions for themselves, preferring other people to decide on their behalf. Documenting decisions on preferred place of death was crucial to see them carried out, but was not always done in practice. Advanced care plans were known to be useful, particularly in care homes, but were not always put in place:
At what point do you record it? Five minutes before they die when they actually don’t want to be moved? Or, a week ago when they said, ‘no, I want to be in hospital, it’s too much trouble for my wife’? Or, in the middle when they haven’t got consciousness so they can’t make a decision? (District nurse)
30
Environmental factors
The physical components of the surrounding environment also affected where people chose as their preferred place of death and whether dying there was appropriate and achievable. The two main subthemes looked at locations and resources.
Locations
Participants discussed the advantages and disadvantages of dying in particular locations. Home was often (but not always) expressed as the preferred place of death by both individuals and their families/carers, particularly earlier on in disease trajectories. The presence of care at home was a major facilitator of this, while poor quality or inappropriate home environments were detrimental. Fluidity was expressed around the concept of home, with importance placed on a homely environment rather than the actual location; this meant that the idea of ‘home’ could be adopted to different settings. Gott notes that people from lower socioeconomic groups equated home with ‘love’ and ‘belonging’, while those from higher socioeconomic groups had more pragmatic concerns about home care:
26
I like it here [care home]. It’s very good. I live here now. This is my home now. (Care home resident)
25
Changing location was often done in response to increasing care needs rather than through personal choice. For care home residents, this was associated with the feeling they were no longer in control of their lives, with staff and family responsible for making key decisions.
35
Hospitals provided the most complex medical care, but in the least personal or homely environment.24,29,32 However, hospital deaths were preferred in some instances, such as among Chinese communities who felt the ongoing healthcare allowed the dying person to maintain a sense of hope.
32
Hospices were seen to provide a high standard of both personal and medical care, but were negatively associated with imminent death among both White and Chinese communities.28,29,32 Hospice care could also be hard to access when most needed, for people across all socioeconomic groups:29,30
… the hospice had been rung but they had no beds which was very sad as he had been in the week before and they were so good. (Bereaved relative)
29
Some people had very limited choice over their place of death, including prisoners. Turner found that staff members generally considered the environment in prisons unsuitable for a dying person.
34
However, potential for compassionate leave was noted, provided the inmate was in the last 3 months of life:
It would be nice if we had somewhere that was slightly more therapeutic than just a prison cell. (Prison staff member)
34
Resources
Place of death was often defined, or limited, by access to particular resources. Some people were denied access to their preferred place of death because the necessary services were not available, with four papers discussing how pressures on services affected access to care.23,24,27,31 This could relate to a lack of equipment, manpower or finance within the health and care services. Gypsy travellers had additional issues with access to health services, even when on settled sites, deterred by cultural preferences and previous negative experiences. 28
The level of care needed by an individual often dictated their place of death despite any previously expressed preferences. Different levels of care were provided in different locations; care homes were able to provide more care than at individuals’ homes but less than hospices and hospitals. The level of care places were able to provide was determined by carer experience level and available equipment. The required level of care changed rapidly as people approached death. Individuals and their carers may have been able to cope in low-care settings up until that point but found managing the final stage difficult. This often meant that access to preferred place of death was denied at the last minute, as a sudden change in care requirements could only be accomplished by a change in location:
when it reaches the final … weeks and days of life when people are very dependent, that is when often it is more difficult to keep people at home when they actually need 24h care. (Community specialist nurse)
27
Discussion
Main findings
This review found that there is limited qualitative evidence on primary socioeconomic factors and preferred place of death in UK literature. Most research focuses on secondary factors such as place of residence and social support, with papers often choosing to focus on particular groups at socioeconomic disadvantage (such as ethnic minorities, prisoners and gypsy travellers) rather than focusing on the impact of socioeconomic status at an individual level. No articles discussed education level/literacy, homelessness or migrants/refugees.
There is a lack of evidence in the included papers that socioeconomic status is a barrier to accessing preferred place of death at an individual level. The only mentioned occurrence of social class having any impact was through the suggestion that people from higher social classes were likely to be more vocal in requesting care. However, this did not guarantee that the desired care would be received; as Kessler notes, people from across different social classes were affected by lack of resources such as the availability of hospice care. 29 The main economic issue noted was the potential loss of earnings of informal carers, which appeared of more concern among higher wage earners than lower wage earners.
Of the socioeconomic factors discussed, the key determinant of whether people were able to die in their preferred place of death was the presence or absence of social support. Almost as important as the number of carers was carer resilience, or the ability of carers to cope with the tasks they were required to perform. In some cases, populations generally perceived as more socioeconomically deprived (such as gypsy travellers) appeared to have more resilient carers, which better enabled an individual to achieve their preferred place of death.
The findings challenge some key concepts about preferred place of death itself. While many people saw ‘home’ as preferred place of death, there was flexibility over what this meant, with the emotional familiarity and presence of loved ones more important than the physical location. These findings gave the idea of ‘home’ certain fluidity and helped explain why preferred place of death often changed to being an individual’s current location if they had been there long enough. This changeability of preferred place of death, particularly in response to crises in care, is important to consider when discussing and documenting end-of-life options with individuals in practice.
Strengths and limitations
This review has systematically synthesised existing literature and included research on a breadth of socioeconomic factors beyond just social status and finance. However, this study does have some limitations. First, focusing on a single health system (United Kingdom) limits the generalisability of the review’s economic findings. However, social and wider factors discussed are relevant across many countries with similar populations and sub-populations. Second, although seven databases were searched, grey literature was not included. Only including peer-reviewed articles increased the quality of the papers used in this review, although it may also have limited the range of studies and data included. The qualitative nature of included papers also meant the number of participants in each individual study was small. Finally, the heterogenous nature of the participants and care settings included in the review potentially makes generalisation difficult. However, it has demonstrated that there are some common factors relevant to all these settings and populations.
What this study adds
Quantitative studies looking at socioeconomic status and palliative care generally demonstrate an association between low socioeconomic status and poorer access to palliative services, including preferred place of death.1–8 However, this synthesis of qualitative research found that participants did not attribute poor access to care to social or economic status at an individual level. This is consistent with recent evidence by Johnson et al., 36 who found no statistically significant difference between the income of bereaved individuals and the decedent’s place of death, even when adjusted for access to palliative care.
The suggestion that availability of social support is the main socioeconomic factor determining place of death has been recognised elsewhere.37–39 The evidence in this review supports the wider literature that suggests preferred place of death is usually, but not always, at home. However, within this broad preference, this study has also shown support for work by Gomes 40 that found preference for home care substantially decreased in the final few weeks of life, supporting Pollock’s 41 view that home may not always be the best place to die. The number of people dying at home has become one of the main quality indicators for successful end-of-life care. 13 However, this research supports the idea that there should be less emphasis on home deaths and more emphasis on providing good quality care across all settings. 42
Although the updated search from May 2018 did not identify any additional papers for inclusion, one of the shortlisted papers covering hospital deaths among South Asian minorities included findings that supported our results. 43 The study replicates the idea that the increasing burden of care during the last few hours of life caused individuals to be transferred from their preferred location of care into hospital. It also highlights key factors discussed in this review that could be addressed in these non-preferred locations to improve the quality of care provided, such as the presence of family and attendance to physical needs.
This review found that methods of looking at socioeconomic status appear to differ between qualitative and quantitative literature. Although social status and income are mentioned, socioeconomic studies in qualitative research look at wider aspects such as ethnicity and other minority groups likely to experience socioeconomic deprivation. This contrasts with quantitative studies that look at socioeconomic status via measures of social class, 29 educational attainment 44 or geographic areas. 45
The review highlights that there is still further work to do on a practical level to ensure preferred place of death is discussed with patients and relatives. This could be improved by wider use of existing resources such as advanced care plans and general practice palliative care registers, although these do not necessarily reflect the dynamic nature of end-of-life decision-making. Collecting this information would also allow further quantitative research to be done on preferred place of death.
Of additional relevance for policymakers is the extent to which the availability of key resources such as care staff and hospice beds also affects access to preferred place of death. Given the importance of social support, this may also be an area of provision worth considering.
The review also suggests that it should be more widely recognised that people’s preferred place of death often changes close to the time of death. In addition, sudden changes in care requirements often require a change in the location of care in order to be accommodated. There also needs to be greater recognition of the fluidity around the concept of ‘home’, where in practice, most individuals’ definition of home refers more to emotions and the presence of loved ones than a physical place. Fleming and Kydd 46 have examined, in more detail, this concept of ‘homeliness’ in care homes, finding that while staff and relatives emphasised standards of care, residents were more interested in the feeling of belonging.
This study has also demonstrated that qualitative syntheses could be used much more widely in public health research. The use of qualitative literature in this case has allowed detailed contextualisation of decision-making at the end of life, which is not possible through quantitative research alone. More research is required looking at the impact of primary socioeconomic factors and preferred place of death at an individual level.
Conclusion
Further qualitative research is needed to explore the barriers and facilitators of access to preferred place of death in socioeconomically deprived UK communities. However, this study has identified human factors such as social support and carer resilience, plus the availability of resources such as care staff and hospice beds, as important factors in achieving preferred place of death. Palliative care policy and research is often rigid in its view of preferred place of death. The findings from this research suggest that both the concept of ‘home’ and the choice of preferred place of death are more fluid. In practice, there needs to be more emphasis on discussing and documenting preferred place of death while also recognising that these preferences may change as death nears or in times of crisis.
Supplemental Material
835146_Appendix_A – Supplemental material for Socioeconomic factors affecting access to preferred place of death: A qualitative evidence synthesis
Supplemental material, 835146_Appendix_A for Socioeconomic factors affecting access to preferred place of death: A qualitative evidence synthesis by Victoria Turner and Kate Flemming in Palliative Medicine
Supplemental Material
835146_Appendix_B – Supplemental material for Socioeconomic factors affecting access to preferred place of death: A qualitative evidence synthesis
Supplemental material, 835146_Appendix_B for Socioeconomic factors affecting access to preferred place of death: A qualitative evidence synthesis by Victoria Turner and Kate Flemming in Palliative Medicine
Footnotes
Acknowledgements
The authors thank Dorothy Mccaughan for her input in shaping the early design and analysis of the research. V.T. determined the initial scope and design of the research; carried out searches, quality appraisal, data analysis and interpretation; and wrote the draft and final versions of the article. K.F. provided guidance on study design, analysis and data interpretation; checked quality appraisal and coding undertaken by V.T.; critically revised article drafts and approved the final version.
Data management and sharing
All the papers included in this review are available through their respective journals.
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.
Ethical approval
No ethical approval was required for this research, as the study was a review of existing published articles with no new primary data collected.
Funding
The author(s) received no financial support for the research, authorship, and/or publication of this article.
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References
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