Psychometric Evaluation of an ICF -Based Instrumental Activities of Daily Living Assessment With Older Adults With Cognitive Decline

Abstract

Importance: Identifying cognitive or physical limitations that contribute to difficulties in instrumental activities of daily living (IADLs) is critical for adequate intervention with community-dwelling older adults with cognitive decline.

Objective: To establish the validity and responsiveness of an IADL scale based on the International Classification of Functioning, Disability and Health (the ICF–IADL) with respect to both cognitive and physical limitations.

Design: Cross-sectional study.

Setting: Multiple community care and senior centers.

Participants: Eighty-two older adults.

Intervention: Combination of physical exercise and cognitive training.

Measures: Five criterion measures—Lawton IADL Scale, Montreal Cognitive Assessment (MoCA), Digit Symbol Substitution Test (DSS), Word Lists Test (WLT), and Timed Up and Go Test (TUG).

Results: The ICF–IADL’s three summary scales—Disability Index (DI), Cognitive Disability Index (CDI), and Physical Disability Index (PDI)—had good concurrent validity with the Lawton IADL Scale. The DI and CDI had moderate to good associations with the MoCA. The DI’s and CDI’s predictive validity for scores on the Lawton IADL Scale, MoCA, and TUG was moderate to good and that of the PDI was fair. Responsiveness was large for the DI, moderate for the CDI, and small for the PDI.

Conclusions and Relevance: The ICF–IADL can be used to measure disability in IADLs related to cognitive and physical limitations. The DI and CDI were better than the PDI in predicting outcomes in general cognitive function and dynamic balance and were more responsive to change after intervention than the PDI.

What This Article Adds: The ICF–IADL addresses both cognitive and physical limitations and can be a valid assessment of IADLs. Occupational therapists can use it to determine difficulties in IADLs and causes of those difficulties, guide treatment planning, and monitor intervention effectiveness with community-dwelling older adults with cognitive decline.

Instrumental activities of daily living (IADLs) are the life skills that are a prerequisite for independent living (Lawton & Brody, 1969). More than half of older adults complain of difficulties with IADLs (Freedman et al., 2014), and these difficulties may be attributable to physical or cognitive decline (Cruz-Jimenez, 2017; Harada et al., 2013). For instance, difficulties with telephone use may be a consequence of poor manual dexterity or trouble remembering how to make calls. To guide clinicians and caregivers in providing appropriate care, IADL assessments should provide not only information about level of independence in specific IADL tasks but also details about the possible limitations resulting from cognitive or physical decline (Ward et al., 1998).

Several IADL scales have been developed to address functional cognitive tasks (e.g., writing, remembering appointments or family occasions), such as the Alzheimer’s Disease Cooperative Study Activities of Daily Living scale (Galasko et al., 1997), the Bayer Activities of Daily Living Scale (Hindmarch et al., 1998), the Everyday Cognition Questionnaire (Farias et al., 2006), and the Functional Activities Questionnaire (Pfeffer et al., 1982). Although most of these scales are used to detect deficits in IADLs related to cognitive impairment among older adults, they do not solely assess performance of IADLs but rather evaluate a mixed spectrum of recreational, personal interaction, and other cognitive abilities. Far less addressed is the assessment of deficits in IADLs with respect to the cognitive and physical abilities they require (Jekel et al., 2015).

To date, an IADL scale developed by Cornelis et al. (2017), which is based on the International Classification of Functioning, Disability and Health (ICF; World Health Organization [WHO], 2002), is the only IADL assessment that addresses the distinction between cognitive and physical impact. The length of the scale (referred to in this article as the ICF–IADL) and its items correspond to those of the Lawton IADL Scale (Lawton & Brody, 1969). The eight items pertain to using a telephone, shopping, food preparation, housekeeping, laundry, mode of transportation, responsibility for one’s own medication, and ability to handle finances. However, for the ICF–IADL, the Lawton IADL Scale’s items were modified to correspond with ICF terminology (WHO, 2002).

In addition, the ICF–IADL uses the ICF scoring system, which rates items on a continuum of capacity and difficulty in performing IADLs, rather than the Lawton IADL Scale’s dichotomous scoring, which divides performance into dependence and independence (Cornelis et al., 2017). Moreover, the ICF–IADL scoring system allows one to assign the potential cause (e.g., cognitive or physical limitations) of the limited IADL performance. The ICF–IADL includes three summary scales: a global disability index (DI), which assesses general IADL performance; a cognitive disability index (CDI), which assesses IADL difficulties with respect to cognitive limitations; and a physical disability index (PDI), which assesses IADL difficulties with respect to physical limitations (Cornelis et al., 2017). The ICF–IADL has excellent interrater reliability and good discriminative validity (Cornelis et al., 2017), but its criterion validity and responsiveness have not been reported.

Valid and responsive measures are required to assess improvement, make decisions, and justify an intervention (Portney & Watkins, 2000). Criterion validity measures how well a new test compares with a well-established criterion test. Predictive validity measures how well a certain measure can predict future behavior (Portney & Watkins, 2000). Responsiveness refers to the ability to detect change, which is an important quality in assessing treatment effects (Husted et al., 2000). The criterion validity and responsiveness of the ICF–ADL, however, have not yet specifically been established among community-dwelling older adults with cognitive decline. In this study, we examined the concurrent validity, predictive validity, and responsiveness of the ICF–IADL for this population.

Method

Participants were enrolled in ongoing randomized controlled trials investigating whether combining aerobic exercise with cognitive training had an effect on cognitive function in older adults with cognitive impairment (Wu, 2018). The inclusion criteria were age 55 yr or older, self- or informant reports of cognitive complaints, Mini-Mental State Examination (MMSE; Folstein et al., 1975) score ≥16, and Barthel Index (Mahoney & Barthel, 1965) score ≥70. Participants with a neurological disorder, severe asthma, joint deformity, or unstable medical condition were excluded.

Participants received one session per week of 45 to 60 min of physical exercise training followed by 45 to 60 min of cognitive training for 12 wk. They were evaluated before and immediately after the interventions. The evaluators were qualified occupational therapists and had at least 3 mo experience evaluating the performance of older adults. They were trained by two authors (I.-C. Chuang and C.-Y. Wu) and completed a competency examination before performing the evaluations. The evaluations were administrated in sequence in 1 hr: Montreal Cognitive Assessment (MoCA; Nasreddine et al., 2005), Word Lists Test (WLT; Tulsky et al., 1997), Digit Symbol Substitution Test (DSS; Tulsky et al., 1997), Timed Up and Go Test (TUG; Podsiadlo & Richardson, 1991), Lawton IADL Scale (Lawton & Brody, 1969), and ICF–IADL. All evaluations except the TUG were administered in a quiet room with a table and chairs. The TUG was assessed in a space that allowed a walking distance of 3 m.

The ICF–IADL was administered by the evaluator in a semistructured interview during which participants were encouraged to describe in detail their state, frequency, and self-perceived changes or limitations on the eight items.

The evaluator assigned scores to the items that were relevant to the participant on the basis of the participant’s narrative and the ICF scoring criteria. Items were scored using a 5-point rating scale (0 = completely independent without any limitation or assistance; 1 = completely independent without help but with mild limitations, performing the activity less frequently, more simplified, more rigid, or less efficiently; 2 = mostly independent, with help sometimes needed, moderate limitations, less adequate, and occasional errors; 3 = completely dependent with continuous help, severe limitations, and many errors; and 4 = complete difficulty or unable to perform). If an item was given a score higher than 0, the evaluator determined the underlying cause of the limitation for this item to be either cognitive (e.g., memory) or physical (e.g., mobility). If the underlying cause of the limitation on an item was both cognitive and physical, the item was assigned the corresponding score for each type of difficulty. If participants responded that an item was irrelevant because they had never performed it or had no need of it, the item was not assigned a score or a type of limitation.

Scores on the three ICF–IADL indexes were then calculated from the item and type of difficulty scores. The global DI score was determined by dividing the sum of scores on all items by the total number of items assigned a score multiplied by 4. The CDI score was determined by dividing the sum of scores on items determined to indicate a cognitive limitation by the total number of items assigned a score. The PDI score was determined by dividing the sum of scores on items determined to indicate a physical limitation by the total number of items assigned a score. All indexes were expressed as percentages, with 0 indicating total independence and higher percentages representing more disability (Cornelis et al., 2017).

Criterion Measures

We used several tools to measure the domains of IADL performance, cognitive function, and physical function at baseline and postintervention:

The Lawton IADL Scale assesses IADL function. Its total score ranges from 0 to 8, with a higher score indicating more independence in IADLs (Lawton & Brody, 1969).

The MoCA is used to measure general cognitive function. It consists of 12 tasks, and the total score ranges from 0 to 30, with a higher score indicating better cognitive function (Nasreddine et al., 2005).

The DSS is a subtest of the Wechsler Adult Intelligence Scale, Third Edition. The total score ranges from 0 to 133, with a higher score indicating better attention (Tulsky et al., 1997).

The WLT is from the Wechsler Memory Scale, Third Edition, and assesses memory. It is used to measure long-term memory capabilities, and scores range from 0 to 100, with a higher percentage indicating better memory (Tulsky et al., 1997).

The TUG evaluates functional mobility and balance. The time to complete this task was recorded, with a longer time indicating poorer performance (Podsiadlo & Richardson, 1991).

Data Analysis

Validity was established by calculating a Pearson correlation coefficient (r). We examined the ICF–IADL’s concurrent validity by correlating scores on the three ICF–IADL indexes with those on the Lawton IADL scale, MoCA, DSS, WLT, and TUG. We examined the predictive validity of the ICF–IADL’s three indexes by correlating scores at baseline with scores on the criterion measures at postintervention. Correlations ranging from 0 to .25 are considered poor; .25 to .5, fair; .5 to .75, moderate to good; and >.75, good to excellent (Portney & Watkins, 2000).

To determine responsiveness, we used the standardized response mean (SRM), calculated by dividing the mean change in the scores by the standard deviation of the changed scores (Liang et al., 1990). We excluded participants with ceiling scores if their DI score was 0 at baseline because these participants had no space for improvement in these scores; we included participants whose DI scores improved after intervention (Karssemeijer et al., 2017). According to the Cohen criteria for effect size, SRM values of 0.2, 0.5, and 0.8 represent small, moderate, and large values for responsiveness, respectively (Cohen, 1988).

Results

Table 1 reports participant characteristics and scores on all measures at preintervention and postintervention. Table 2 summarizes the concurrent validity of the three ICF–IADL indexes and all criterion measures. The negative correlations between the DI, CDI, and PDI and the Lawton IADL Scale (rs = −.948, −.883, and −.503, respectively; p < .01) demonstrate the ICF–IADL’s concurrent validity with respect to IADL function. Its concurrent validity with respect to cognitive limitations is demonstrated by the cognitive measures’ negative correlations with the DI (rs = −.567 to −.435, p < .01), CDI (rs = −.519 to −.385, p < .01), and PDI (rs = −.259 to −.323, p < .05). The ICF–IADL’s concurrent validity with respect to physical limitations is shown by the TUG’s positive correlation with the DI (r = .584, p < .01), CDI (r = .501, p < .01), and PDI (r = .475, p < .05).

Table 1.

Participant Characteristics and Measurement Results

Characteristics and Measures	Preintervention		Postintervention
Characteristics and Measures	M	SD	M	SD
Age, yr	74.03	7.33	—	—
Education, yr	9.06	3.89	—	—
Gender, n (%)
Male	26	(31.70)	—	—
Female	56	(68.30)	—	—
Measure
MMSE	26.32	3.53	—	—
DI	7.89	17.05	5.11	11.28
CDI	4.99	14.09	2.36	7.29
PDI	3.61	9.41	2.90	8.34
Lawton IADL scale	7.44	1.33	7.66	0.93
MoCA	23.24	5.02	24.24	4.74
DSS	39.59	19.20	42.66	20.20
WLT	49.45	35.46	59.99	32.16
TUG	12.19	4.50	11.49	3.40

Note. N = 82 for all correlations except for the TUG. The TUG was used to assess only 57 older adults because the space in the remaining 25 older adults’ surroundings was insufficient for them to perform this test. — = not applicable; CDI = Cognitive Disability Index; DI = Disability Index; DSS = Digit Symbol Substitution Test; IADL = instrumental activities of daily living; MMSE = Mini-Mental State Examination; MoCA = Montreal Cognitive Assessment; PDI = Physical Disability Index; TUG = Timed Up and Go Test; WLT = Word Lists Test.

Table 2.

Concurrent Validity of the ICF–IADL

Variable	Lawton IADL Scale	MoCA	DSS	WLT	TUG
DI	−.948**	−.567**	−.452**	−.435**	.584**
CDI	−.883**	−.519**	−.385**	−.402**	.501**
PDI	−.503**	−.259*	−.323**	−.278*	.475**

Note. N = 82 for all correlations except those for the TUG (N = 57). The TUG was used to assess only 57 older adults because the space in the remaining 25 older adults’ surroundings was insufficient for them to perform this test. CDI = Cognitive Disability Index; DI = Disability Index; DSS = Digit Symbol Substitution Test; IADL = instrumental activities of daily living; ICF–IADL = instrumental activities of daily living scale based on the International Classification of Functioning, Disability and Health; MoCA = Montreal Cognitive Assessment; PDI = Physical Disability Index; TUG = Timed Up and Go Test; WLT = Word Lists Test.

p < .05. **p < .01.

Table 3 summarizes the predictive validity of the ICF–IADL indexes measured at baseline with respect to all criterion measures at the postintervention assessment. All ICF–IADL indexes were significantly correlated with the Lawton IADL Scale (rs = −.574 to −.804, p < .01), MoCA (DI, r = –.517, p < .01; CDI, r = –.497, p < .01; PDI, r = −.247, p < .05), DSS (DI, r = –.380, p < .01; CDI, r = –.318, p < .01; PDI, r = −.269, p < .05), WLT (rs = −.290 to −.437, p < .01), and TUG (rs = .404 to .606, p < .01).

Table 3.

Predictive Validity of the ICF–IADL

Variable	Lawton IADL Scale	MoCA	DSS	WLT	TUG
DI	−0.804**	−0.517**	−0.380**	−0.437**	0.606**
CDI	−0.729**	−0.497**	−0.318**	−0.422**	0.526**
PDI	−0.574**	−0.247*	−0.269*	−0.290**	0.404**

Note. N = 82 for all correlations except those for the TUG. The TUG was used to assess only 57 older adults because the space in the remaining 25 older adults’ surroundings was insufficient for them to perform this test. CDI = Cognitive Disability Index; DI = Disability Index; DSS = Digit Symbol Substitution Test; ICF–IADL = instrumental activities of daily living scale based on the International Classification of Functioning, Disability and Health; MoCA = Montreal Cognitive Assessment; PDI = Physical Disability Index; TUG = Timed Up and Go Test; WLT = Word Lists Test.

p < .05. **p < .01.

At baseline, 50% of the participants achieved the maximum score (0) on the DI. We calculated the responsiveness of the ICF–IADL for the 25 participants whose DI scores improved. Responsiveness was large for the DI (SRM = .82), moderate for the CDI (SRM = .66), and small for the PDI (SRM = .23).

Discussion

To the best of our knowledge, this is the first study to investigate the criterion validity and responsiveness of the ICF–IADL with respect to both cognitive and physical limitations. This study extends the previous investigation (Cornelis et al., 2017) of the reliability and discriminant validity of this scale to other types of validity and responsiveness. Our findings may support the use of the ICF–IADL by clinicians and researchers as a measure to evaluate cognitive and physical impacts on IADL performance among community-dwelling older adults with cognitive decline.

Concurrent correlations between the DI, CDI, and PDI and the Lawton IADL Scale were moderate to excellent, suggesting that the three ICF–IADL indexes could identify disability in IADLs among community-dwelling older adults with cognitive decline.

The DI and CDI had moderate to good negative associations with the MoCA, and the PDI had a fair negative association, indicating that the more severe participants’ IADL disability was as a result of overall or cognitive limitation, the more cognitive deficits participants had, as assessed with objective measures. The PDI may assess IADL difficulties related to physical problems rather than general cognitive abilities.

The three ICF–IADL indexes significantly correlated with the DSS and WLT with a fair degree of magnitude. Our findings show that difficulties in IADLs evaluated with the ICF–ADL were modestly associated with cognitive processing speed and memory capacity. This is not surprising because IADLs are sophisticated tasks that require more than a single cognitive ability. IADL ability is determined by multiple factors that are best assessed by synthesizing information about attention, memory, executive function, depression, health status, and demographic variables (Royall et al., 2007).

The positive correlations between the three ICF–IADL indexes and the TUG were moderate to good. Given that physical ability is required to perform the functional tasks involved in many complicated daily activities, such as transportation and shopping, these indexes should be related to mobility and balance, as represented by the TUG. An interesting finding is that the relationship between the CDI and the TUG, like that between the PDI and the TUG, was moderate to good, although the TUG is generally thought to reflect physical ability. This result is in line with the findings of previous studies demonstrating positive correlations between the TUG and deficits in executive function, memory, and processing speed (Donoghue et al., 2012) and with functional limitations in cognitively demanding IADLs (Donoghue et al., 2014).

Regarding predictive ability, preintervention DI scores had moderate to excellent correlations with postintervention Lawton IADL Scale, MoCA, and TUG scores but fair correlations with the DSS and WLT, demonstrating good predictive ability for performance in IADL function, general cognitive function, and dynamic balance and fair predictive ability for specific cognitive function after the intervention. Correlations between preintervention DI and CDI scores and the postintervention criterion measures tended to be better than those between the PDI and these criterion measures, suggesting that overall and cognitive disability might be better postintervention indicators of general performance of IADLs and functional mobility than physical disability.

Our results showed that the DI was highly responsive to IADL changes after the intervention, whereas the CDI was moderately responsive and the PDI was less responsive, suggesting that a plausible use of the ICF–IADL may be to detect changes in IADL performance as a result of a cognitive-based intervention. The DI would be the best of the three indexes to assess changes in IADL performance after an intervention.

Limitations

The ICF–IADL is a self-report measure that assesses older adults’ perceptions of their own functioning, and they may sometimes over- or underestimate this functioning. ICF–IADL results may be affected by the presence of cognitive impairment or depression, language, education, and culture. However, the reasonable concurrent validity between the CDI and cognitive function as measured by performance-based tests demonstrated that these self-report results are reliable.

The sample size for the TUG was smaller because a few assessment settings did not have the space in which to conduct it, resulting in missing data. However, the results of the correlational analysis of the TUG and the other variables still showed significant differences, indicating that the statistical power should be appropriate to detect a relationship between them. The smaller sample size for the TUG may not be a confounder or bias the results.

This study included only older adults with a MMSE score of 16 or more. A larger sample of community-dwelling older adults with different characteristics, such as different levels of cognitive or motor impairment, is needed to verify the results.

Implications for Occupational Therapy Practice

The findings of this study have the following implications for occupational therapy practice:

The ICF–IADL addresses both cognitive and physical limitations and can be a valid assessment of IADLs.

Occupational therapy practitioners can use the DI and CDI to predict general cognitive function and functional mobility and balance among community-dwelling older adults after a combined cognitive–exercise intervention.

The DI and CDI can be used to detect a change in IADLs resulting from an intervention among community-dwelling older adults.

The ICF–IADL can be used to determine difficulties in IADLs and causes of those difficulties, guide treatment planning, and monitor intervention effectiveness.

Conclusion

This is the first study to explore the ICF–IADL’s concurrent validity with respect to both cognitive and physical disabilities, predictive validity, and responsiveness among older adults with cognitive decline. This study, together with the Cornelis et al. (2017) study, demonstrates the sound psychometric properties supporting the use of the ICF–IADL scale to distinguish between cognitive and physical impacts on IADLs. This study demonstrates that the ICF–IADL has reasonable concurrent validity and provides support for the use of the DI, CDI, and PDI to measure disability in IADLs related to cognitive and physical limitations. The three ICF–IADL indexes all predicted the outcome of the IADL intervention, and the DI and CDI were better than the PDI in predicting outcomes pertaining to general cognitive function and dynamic balance. The DI and CDI were more responsive to change after the intervention than the PDI. However, additional study with a larger sample of community-dwelling older adults with different characteristics, such as different levels of cognitive or motor impairment, is needed to verify the results.

Footnotes

Acknowledgments

Hui-Yan Chiau and Ching-Yi Wu contributed equally to this work. This study was supported in part by Chang Gung Memorial Hospital (CMRPD1E0281-0283, CMRPD1F0411-0413), the Healthy Aging Research Center at Chang Gung University through the Featured Areas Research Center Program within the Framework of the Higher Education Sprout Project by the Ministry of Education (EMRPD1I0451), and the Ministry of Science and Technology (MOST 106-2314-B-182-024-MY3, MOST107-2811-B-182-516) in Taiwan. The study is registered at (NCT03619577).

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