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24-12-2019 | Review | Uitgave 6/2020 Open Access

Quality of Life Research 6/2020

Capability instruments in economic evaluations of health-related interventions: a comparative review of the literature

Tijdschrift:
Quality of Life Research > Uitgave 6/2020
Auteurs:
Timea Mariann Helter, Joanna Coast, Agata Łaszewska, Tanja Stamm, Judit Simon
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Background

Economic evaluations assess whether an intervention provides value for money through the comparative analysis of alternative courses of action in terms of both costs and consequences [ 1]. The assessment of consequences in economic evaluation requires information about their identification (what), measurement (how much) and valuation (how valuable) [ 2]. Standard methods of health economic evaluations identify outcomes based on a rather narrow definition of health that aims to express outcomes in Quality-Adjusted Life Years (QALYs). However, there are many interventions, particularly in the areas of mental health, end-of-life care, public health and social care, where the impacts of interventions go beyond this narrow view of health. The contemporary literature (e.g. [ 36]) recognises the need to move away from the standard methods for assessing effects of interventions and toward incorporating outcomes beyond the QALY framework, when producing an economic evaluation which feeds into decision making about resource allocation in health-related interventions. The most promising approach to address this issue is the application of Sen’s capability framework, which was introduced by Sen [ 7] in the early 1980s as an alternative to standard utilitarian welfare economics. The core focus of the capability approach is on what individuals are able to be and do in their lives (i.e. capable of). The application of the capability approach in health economics has gained popularity because it potentially provides a richer evaluative space for the evaluation of interventions [ 8].
There has been increasing interest in developing instruments for using the capability approach in the measurement and valuation of outcomes for health economic evaluations. Capability instruments have been in the public domain for over a decade and publications have started to shift from methodological issues towards use of the measures within economic evaluations. Some decision-making institutions currently recommend the inclusion of capability measures in economic evaluations in certain contexts. The Zorginstituut in the Netherlands [ 9] recommends the inclusion of ICEpop CAPability measure for Older people (ICECAP-O) alongside the EuroQol instrument (EQ-5D) for the evaluation of interventions in long-term care, where the relevant outcomes extend beyond health. The most recent methods guideline [ 10] of the National Institute for Health and Care Excellence (NICE) acknowledges that the intended outcomes of interventions go beyond changes in health status for some decision problems; hence, ‘broader, preference weighted measures of outcomes, based on specific instruments, may be more appropriate…’ and ‘the economic analysis may also consider effects in terms of capability and well-being’ (p. 137). The manual specifically recommends the Adult Social Care Outcomes Toolkit (ASCOT) and ICECAP-O instruments.
However, the choice between instruments and their practical application in particular contexts lack a systematic approach. For instance, the ICECAP-O recommended by NICE is targeted at a subgroup of the population (older adults), whilst the ASCOT was specifically developed for the assessment of social care interventions. A recent review of the literature examined current trends in the application of ICECAP-O [ 11]. The authors found that the ICECAP-O has mainly been included as a secondary economic measure and the reporting of results is brief with minimal detail and often no discussion or interpretation. An overview of the psychometric properties of all potential capabilities instruments and their usefulness for economic evaluations would contribute to providing a clear guidance. This could later be used as a reference point for future comparative analysis of policies or interventions. Hence, the main aim of this paper is to synthesise the current evidence about the application of capability instruments in health economic evaluations. This translates into the following objectives: (i) to summarise information about the development, psychometric properties and preference valuation of relevant capability instruments; (ii) to compare the identified capability instruments in terms of their psychometric properties and up-to-date application in health economic evaluations; (iii) to identify applied evaluations that have used the capability-based approach in health economic evaluations and (iv) to pinpoint the challenges and considerations in the application of the capability approach in economic evaluations of health-related interventions.

Methods

Identification of relevant studies

The identification of papers was based on two main approaches: a traditional systematic literature search and a comprehensive pearl growing method [ 12]. The grey literature search in Google Advance either generated an unmanageable number of hits due to the term “capability” being used across a number of disciplines with varying meanings, as well as having generic lay use and interpretation of the term; or there was no addition to the search of other databases when more precise terms were used. As the development and validation of the capability approach in health economics currently appears to be concentrated among a limited group of researchers, as an additional step, websites dedicated to the instruments identified through the systematic search were specifically targeted and reviewed for relevant information.

Systematic literature search

Firstly, we conducted a systematic literature search. Search terms combined expressions for economic evaluation and frequently used terms for the capability approach, including synonyms and names of instruments most well-known in the area of health economics. Search terms are presented in Appendix 1. The selection of databases was based on similar reviews of health measures (PROMs) [ 6, 13] in the area and included Embase, Medline, Web of Science, Psychinfo and Scopus. The literature search was conducted on 1 February 2019 and the review was limited to the last 20 years when the first publications in this topic area appeared [ 14]. Relevant systematic literature reviews were searched for further references and their findings were kept for comparison and discussion.

Comprehensive pearl growing method

The term ‘capability’ produces very broad ranging results when used as a search term due to its wide range of meanings, including lay meanings. The so-called comprehensive pearl growing method [ 12] is a technique used to ensure all relevant articles are included, particularly in case of issues with vocabulary in a search strategy. This method is particularly useful in interdisciplinary research and where recent developments are expected in the literature. The process of pearl growing commences with the identification of ‘key pearls’ (i.e. key studies), that can be identified from within the literature as being compatible with the aim of the review [ 12]. Once the key pearls have been identified, these are used to generate the ‘first wave of pearls’, that is, papers that have cited the key pearls within their reference list. It has been used successfully in a different type of review in the context of capabilities [ 13]. This second approach was implemented to validate the strategy applied during the systematic search and to identify potential further papers.
Two waves of the pearl growing method were conducted: one focusing on the development of instruments and a second wave related to the application of the instruments. A third wave was deemed unnecessary because the identified last generation of seminal papers were published only recently and have not been cited yet. The results are presented in Table  1. The first wave used for citation searching were the developmental studies of the four most commonly used and reported capability instruments: ASCOT, ICECAP-O, its version for adults (ICECAP-A) and the Oxford CAPabilities questionnaire-Mental Health (OxCAP-MH). The second wave relied on the three main papers from the last 5 years (but already with some relevant citations) that aimed to identify recent developments and up-to-date knowledge in the application of the capability approach in health economic evaluations. The number of citations was retrieved from Scopus on 14 March 2019.
Table 1
Key pearls for the two waves of the comprehensive pearl growing method
Wave
Study
Number of citations
Short description
Wave 1
[ 52]
92
Development of the ASCOT
[ 53]
146
Development of the ICECAP-A
[ 54]
158
Development of the ICECAP-O
[ 39]
66
Development of the OxCAP-MH
Wave 2
[ 48]
27
Description of new methods to conduct economic evaluations using the capability approach
[ 55]
13
Presents the opportunities and challenges of the capability approach in health economics
[ 49]
4
Critical review of relevant questionnaires to measure and value capability

Study selection

Titles and abstracts were sifted by two researchers (TL and AL) and studies were included for further assessment if they met the following inclusion criteria: (1) Full paper available in English or German languages. (2) Scope of study is the a rea of health or health- related interventions, including any interventions specifically targeting the promotion of health and prevention and treatment of ill-health irrespective of the sector where these were implemented. Hence, our study also included potentially relevant studies from the social care and public health sectors. (3) Focus of research is the evaluation or assessment of the outcomes of interventions using the capability approach. (4) Paper includes information on the use (or recommended use) of the capability approach in economic evaluations. (5) Paper is an applied evaluation OR focuses on the development, psychometric validation (or comparison to other tools) or preference valuation of instruments.
The full paper was retrieved if a study met the inclusion criteria based on its title and abstract. Consequently, full papers were assessed by two researchers (TH and AL) for inclusion based on their contribution to at least one of the aims of this literature review and subsequently allocated to the categories of either (i) applied evaluations (using a capability instrument in a completed economic evaluation) or (ii, iii, iv, v) methods papers. Methods papers were further categorised based on their relevance to the identification, measurement and valuation of outcomes, as well as the practical application of tools and theoretical contributions. Papers were grouped into categories of (ii) instrument development, (iii) psychometric validation or quantitative comparison of instruments, (iv) preference valuation of instruments and (v) methods for incorporation of the capability approach in economic evaluations. The latter one includes potential fields of application, approaches to use the results, incorporation of the results into a potential framework, for instance, Capability-Adjusted Life Years (CALYs), years of full capability or years of sufficient capability equivalence, etc. Some of the studies with significant theoretical contributions to the application of the capability approach in health economic evaluations which did not fit the above criteria were noted for discussion.
No specific quality assessment was applied, all studies which provided information on either the psychometric properties or use of capabilities instruments in economic evaluations were included. The instruments were assessed based on their psychometric properties according to the COSMIN checklist [ 15], feasibility [ 16], potential for transferability and evidence regarding valuation.

Data extraction and analysis

Separate data extraction forms were created for empirical and psychometric evaluation (and other methods) studies. The search for information on valuation included any kind of preference-based valuation of instruments (or their dimensions/domains) and the existence of value sets. Further information on data extraction is presented in Appendix 2.
Trends in the literature were analysed based on the number of different types of studies published each year. The information elicited from the studies was structured according to the capability instrument in question. Information about economic evaluations, and the psychometric properties and correlation coefficients from studies comparing instruments are presented in review tables. Due to the variability of methods used in the validation and comparison studies, only narrative synthesis, including tabulation and frequency analyses, was conducted as no statistical pooling was possible. The information gathered was synthesised in a qualitative rather than quantitative manner by TH.

Results

Search results

The literature search identified 98 studies for inclusion (Appendix 4 provides a complete list). The pearl growing method identified 29 citations beyond those captured by the systematic search strategy. However, none of the additional references met the inclusion criteria, and the papers included in this review were actually all picked up by the systematic search. An overview of the literature search based on the PRISMA statement is presented in Fig.  1.
The increasing number of relevant publications in recent years is a clear trend (shown in Fig.  2). A further trend also appears to be a shift from developmental studies towards the validation of capability instruments and their use in empirical studies.

Instruments to assess capability

Development of instruments

The literature review identified 14 capability instruments. Table  2 shows the heterogeneity of the capability instruments in terms of development methods, disease areas, types of interventions, population groups and the questionnaire structure.
Table 2
Overview of the main characteristics and development methods of instruments that measure and value capability for economic evaluations in health
Instrument
Instrument full name
Field
Population
Number of
Development method
Informants
Number of informants
References
Dimensions
Levels
ACQ‐CMH‐104
Achieved Capabilities Questionnaire for Community Mental Health
Mental health
Patients
104
Unknown
Focus groups
Participants of Portuguese community mental health services
50
[ 56]
ASCOT
Adult Social Care Outcomes Toolkit
Social care
Patients
8
4
Delphi exercise, Literature review and expert opinion, Further improvement of the Older People’s Utility Scale (OPUS)
Experts and service users
330
[ 52]
ASCOT Easy Read version
Easy Read Version of the Adult Social Care Outcomes Toolkit
Social care
People w. intellectual disabilities
8
4
Focus groups and in-depth interviews
Intellectual disability or autism
54
[ 57]
ASCOT – proxy version
Proxy-report version of the Adult Social Care Outcomes Toolkit
Social care
Patients
8
4
In-depth qualitative interviews
Adult care workers or unpaid family carers of patients with cognitive and/or communication impairments
25
[ 58]
ASCOT-Carer
Carer Version of Adult Social Care Outcomes Toolkit
Social care
Carers
7
4
Literature review and feedback from service users, carers, practitioners and policy-makers
Service users, carers, practitioners and policy-makers
31
[ 59]
CAF
Currently Achieved Functioning
General
Older people
5
5
In-depth qualitative interviews
Older people living in 3 Dutch urban areas
99
[ 60]
ICECAP-A
ICEpop CAPability measure for Adults
General
General public
5
4
In-depth, informant-led, interviews
General public (purposively selected through a random electoral sample)
36
[ 53]
ICECAP-CPM
ICEpop CAPability Close Person Measure
End of life
Close persons
6
5
In-depth qualitative interviews
Bereaved within the last 2 years or with a close person currently receiving end-of-life care
27
[ 61]
ICECAP-O
ICEpop CAPability measure for Older people
General
Older people
5
4
In-depth qualitative interviews
Purposively selected informants aged 65 and over in private households
40
[ 54]
ICECAP-SCM
ICEpop CAPability Supportive Care Measure
End of life
Patients
7
4
In-depth qualitative interviews
Older people from different groups across the dying trajectory
23
[ 62]
OCAP-18
OCAP-18
Public health
General public
18
Unknown
Theoretical framework,
Focus groups and in-depth interviews
Purposively sampled from various community groups in Glasgow, United Kingdom
40
[ 63]
OxCAP-MH
Oxford Capabilities Questionnaire for Mental Health
Mental health
Patients
16
5
Theoretical framework,
Focus group discussions
Psychiatrists, Psychologists, Social scientists, Health economists
336
[ 39]
(Low-income questionnaire)
(Low-income questionnaire)
Low-income settings
General public
6
Unknown
Focus groups
Women in rural Malawi
129
[ 64]
(Chronic pain questionnaire)
(Chronic pain questionnaire)
Chronic pain
Patients
8
Unknown
Focus groups and in-depth interviews
Respondents were recruited through a Pain Management Clinic in the East of England
16
[ 65]

Availability of evidence on the characteristics of capability instruments

As Table  3 demonstrates, there is at least some evidence about the psychometric properties of most instruments.
Table 3
Availability of evidence on the characteristics of capability instruments for health economic evaluations
Instrument
Reliability
Validity
Responsiveness
Interpretability/Feasibility
Valuation
ACQ‐CMH‐104
[ 66]
[ 66]
Unknown
Unknown
Unknown
ASCOT
[ 67]
[ 21, 68, 69, 70, 71, 72, 73, 74]
[ 71]
[ 75]
[ 52]
ASCOT easy read
Unknown
Unknown
Unknown
[ 57]
Unknown
ASCOT-proxy
Unknown
Unknown
Unknown
[ 58]
Unknown
ASCOT-carer
[ 76]
[ 76]
Unknown
Unknown
Unknown
CAF
Unknown
Unknown
Unknown
[ 60]
Unknown
ICECAP-A
[ 77]
[ 20, 23, 24, 27, 33, 34, 38, 78, 79, 80]
[ 23, 32, 33, 34, 37, 81]
[ 82, 83, 84]
[ 85]
ICECAP-CPM
Unknown
Unknown
Unknown
Unknown
Unknown
ICECAP-O
[ 30, 86, 87]
[ 18, 21, 22, 25, 26, 40, 74, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96]
[ 26, 31, 35, 36, 95, 97]
[ 25, 26, 30, 40, 89, 91, 98, 99]
[ 88]
ICECAP-SCM
Unknown
Unknown
Unknown
[ 29, 83]
[ 100, 101]
low-income Q
Unknown
[ 102]
Unknown
Unknown
Unknown
pain Q
Unknown
Unknown
Unknown
Unknown
Unknown
OCAP-18
Unknown
Unknown
Unknown
Unknown
Unknown
OxCAP-MH
[ 17, 19, 103]
[ 17, 19, 103]
[ 17]
[ 39]
Unknown
The most recently developed instruments, unsurprisingly, have less information available about their reliability, validity and responsiveness; an exception is OCAP-18 which was among the first capability instruments to be developed, but for which there is no further psychometric evidence available. The main difference across different groups of capability instruments is whether valuations that reflect the preferences of patients or the general public are available. The ASCOT and most ICECAP instruments have reported valuation studies and are therefore considered to possess evidence regarding their ability to reflect values of informants, whilst this is currently missing, for instance, for OxCAP-MH.

Different language versions of instruments

Apart from ACQ‐CMH‐104, all instruments were originally developed in English. The ASCOT, ICECAP-A, ICECAP-O and OxCAP-MH instruments have been translated to further languages, and these new versions have been validated (Table  4).
Table 4
Availability of different language versions of capability instruments
Instrument
Availability of language versions beside English a
ACQ‐CMH‐104
Only available in Portuguese language
ASCOT
Japanese [ 105]; Dutch [ 106]
ASCOT easy read
None identified
ASCOT-proxy
None identified
ASCOT-carer
None identified
CAF
None identified
ICECAP-A
Chinese [ 107], Danish (unpublished), Dutch (unpublished), German [ 107], Italian (unpublished), Persian (unpublished), Welsh (unpublished)
ICECAP-CPM
none identified
ICECAP-O
Chinese (unpublished), Dutch [ 92], French (unpublished), German [ 18], Spanish [ 87], Swedish [ 86], Welsh (unpublished); Italian, Norwegian and Portuguese [ 109]
ICECAP-SCM
None identified
low-income Q
None identified
pain Q
None identified
OCAP-18
None identified
OxCAP-MH
German [ 103]
aInformation on unpublished translations of instruments stem from the dedicated websites of the instruments

Validation of capability instruments

Reliability
The test–retest reliability of most instruments have been successfully assessed in some groups of population, e.g. ACQ‐CMH‐104 [ 56]; ASCOT [ 72]; ICECAP-A [ 77]; ICECAP-O [ 86]; OxCAP-MH [ 19].
Validity
There were 25 studies among the included papers that used Pearson’s or Spearman rank correlation coefficients to quantitatively assess the validity of all language versions of the capability instruments and/or compare it to other instruments. Quantitative evidence was provided on the validity of six capability instruments, including ACQ‐CMH‐104, ASCOT, ICECAP-A, ICECAP-O, OxCAP-MH and Women’s Capabilities Index. Table  5 (and Appendix 5) summarise the correlations.
Table 5
Construct validity of capability instruments for health economic evaluations
Capabilities instrument
Compared with… (full names in Appendix 5)
Value of correlation*
Population (country in Appendix 5)
Number of informants
References
ACQ‐CMH‐104
RAS
0.46*
Psychiatric patients
92
[ 66]
WHOQOL‐Bref
0.60*
Psychiatric patients
129
[ 66]
ASCOT
Barthel Index
0.45
Older social care users
205
[ 21]
Cantril’s Ladder
0.66
Older social care users
205
[ 21]
CASP-12
0.58
Older home care residents
301
[ 52]
EQ-5D-3L
0.41
Older home care residents
301
[ 52]
EQ-5D-3L
0.40
Older home care residents
301
[ 70]
EQ-5D-3L
0.47
Older home care residents
224
[ 68]
EQ-5D-3L
0.41*
Frail older adults living at home
190
[ 74]
EQ-5D-3L
0.37
Older social care users
748
[ 72]
EQ-5D-5L
0.63
Older social care users
205
[ 21]
EQ-5D-5L
0.24
Older adults in a day rehabilitation facility
22
[ 71]
EQ-5D-VAS
0.64
Older social care users
205
[ 21]
GDS-15
− 0.69
Older social care users
205
[ 21]
GHQ-12
−  0.58
Older home care residents
301
[ 52]
ICECAP-A
0.62
Older social care users
748
[ 72]
ICECAP-O
0.81
Older social care users
205
[ 21]
ICECAP-O
0.41*
Frail older adults living at home
190
[ 74]
ICECAP-O
0.67
Older social care users
748
[ 72]
OPQOL-13
0.76
Older social care users
205
[ 21]
OPQOL-brief
0.38
Older adults in a day rehabilitation facility
22
[ 71]
OPQoL-Brief
0.58
Older social care users
87
[ 69]
SWLS
0.74
Older social care users
205
[ 21]
ASCOT-Carer
CES
0.58
Social care recipients
376
[ 76]
CSI
− 0.59
Social care recipients
384
[ 76]
EQ-5D-3L
0.34
Social care recipients
382
[ 76]
QoL
0.62
Social care recipients
384
[ 76]
ICECAP-A
15D
0.50*
Healthy general public and patients from 8 disease areas
6756
[ 24]
AQoL-8D
0.31*
Healthy general public and patients from 8 disease areas
6756
[ 24]
AQoL-8D
0.80
Healthy general public and patients with 7 chronic conditions
8022
[ 20]
EQ-5D-3L
0.53
Women with lower urinary tract infection
478
[ 23]
EQ-5D-3L
0.49
Knee pain patients in primary care
500
[ 27]
EQ-5D-5L
0.62*
Healthy general public and patients with 7 chronic conditions
1212
[ 108]
EQ-5D-5L
0.49*
Healthy general public and patients from 8 disease areas
6756
[ 24]
EQ-5D-5L
0.60
Healthy general public and patients with 7 chronic conditions
8022
[ 20]
HUI-3
0.32*
Healthy general public and patients from 8 disease areas
6756
[ 24]
LDQ
−  0.48
Opiate substitution recipients
83
[ 34]
SF-6D
0.64*
Healthy general public and patients with 7 chronic conditions
1212
[ 108]
SF-6D
0.47*
Healthy general public and patients from 8 disease areas
6756
[ 24]
SSQ
0.43
Opiate substitution recipients
83
[ 34]
SWLS
0.66*
Healthy general public and patients with 7 chronic conditions
1212
[ 108]
ICECAP-O
ADRQL
0.53*
Nursing home residents with dementia
95
[ 18]
Barthel Index
0.49
Older social care users
209
[ 21]
Barthel Index
0.72*
Nursing home residents with dementia
95
[ 18]
Cantril’s Ladder
0.74
Older social care users
213
[ 21]
CTM-3
0.23
Patients from outpatient day rehabilitation unit
82
[ 22]
EQ-5D-3L
0.34
Older people with hip fracture
113
[ 95]
EQ-5D-3L
0.69*
Nursing home residents with dementia
95
[ 18]
EQ-5D-3L
0.53
Older people after hip fracture surgery
87
[ 93]
EQ-5D-3L
0.44
Patients from outpatient day rehabilitation unit
80
[ 22]
EQ-5D-3L
0.47
Patients visiting the clinic
215
[ 25]
EQ-5D-3L
0.63
Frail older adults living at home
190
[ 74]
EQ-5D-5L
0.68
Older social care users
207
[ 21]
EQ-5D-5L
0.63
General population aged 70 or older
516
[ 90]
EQ-5D-VAS
0.66
Older social care users
208
[ 21]
GDS-15
− 0.73
Older social care users
210
[ 21]
OHS
0.38
Older people with hip fracture
113
[ 95]
OPQOL-13
0.80
Older social care users
211
[ 21]
SWLS
0.82
Older social care users
212
[ 21]
ICECAP-O family version
EQ-5D family version
0.57*
Nursing professionals of psycho-geriatric elderly
96
[ 92]
EQ-VAS family version
0.43*
Family members of psycho-geriatric elderly
68
[ 92]
ICECAP-O nursing version
EQ-5D nursing version
0.48*
Nursing professionals of psycho-geriatric elderly
96
[ 92]
EQ-VAS nursing version
0.55*
Family members of psycho-geriatric elderly
68
[ 92]
OxCAP-MH
BPRS
−  0.41
Patients with psychosis
172
[ 19]
BSI-18
− 0.67*
Patients in socio-psychiatric services
162
[ 17]
EQ-5D VAS
0.58*
Patients in socio-psychiatric services
161
[ 17]
EQ-5D-3L
0.45
Patients with psychosis
172
[ 19]
EQ-5D-5L
0.66*
Patients in socio-psychiatric services
160
[ 17]
EQ-5D-VAS
0.52
Patients with psychosis
172
[ 19]
GAF
0.24
Patients with psychosis
172
[ 19]
GAF
0.35*
Patients in socio-psychiatric services
168
[ 17]
Mini-ICF-APP
−  0.47*
Patients in socio-psychiatric services
167
[ 17]
SIX
0.12
Patients with psychosis
172
[ 19]
WHOQOL-Bref Environment
0.69*
Patients in socio-psychiatric services
166
[ 17]
WHOQOL-BREF Physical health
0.69*
Patients in socio-psychiatric services
163
[ 17]
WHOQOL-Bref Psychological
0.75*
Patients in socio-psychiatric services
164
[ 17]
WHOQOL-Bref Social relationships
0.50
Patients in socio-psychiatric services
165
[ 17]
Women’s Capabilities Index
WHOQOL-Bref
0.62*
Women from Malawi
20
[ 64]
Values in italic are Pearson’s coefficients, values in standard writing are Spearman rank correlations. A * behind the value means that the study used a non-English version of the capability instrument
There is variation between studies in the correlation measures used, the instruments compared, the characteristics of the population, number of informants, testing of hypotheses generated regarding likely associations between the data and testing across known groups for discriminant and convergent validity. Hence, it is difficult to provide general statements about the comparison of capability instruments with other PROMs, or to conduct statistical pooling of the results. High correlation estimates (above 0.8) were found between capability instruments: ASCOT/ICECAP-O [ 49] and ICECAP-A/AQoL-8D [ 20].
The examined studies provided very diverse estimates for the correlations between Health-related Quality of Life (HRQoL) and the different capability instruments. Most studies compared the ASCOT, ICECAP-A and ICECAP-O instruments with either disease-specific or generic HRQoL instruments. A wide range of disease-specific instruments were applied across studies, mainly being used when informants consisted of patients and social care recipients. EQ-5D-3L/-5L was used in 92% ( n = 23) of the included validation and comparison studies as a HRQoL measure. In most cases, the 5L version of the EQ-5D instruments provided higher correlation coefficients compared to the 3L version. The higher correlation with capability instruments could be explained by lower ceiling effects and higher sensitivity to minor changes in the 5L version compared to the 3L version.
There seem to be a consensus in the literature that the capability approach provides complementary information to HRQoL measures. However, capability instruments could also be perceived as enhanced rather than complementary to the narrow interpretation of well-being/quality of life when focusing only on HRQoL. Most studies [ 2527] found that the ICECAP and EQ-5D instruments provide complementary information, and a mapping is not recommended between them. Engel et al. [ 24] found that the ICECAP-A provides evidence above that gathered from most commonly used preference-based HRQoL instruments. Similar findings were reported for other capability instruments. Forder and Caiels [ 68] found that ASCOT has greater validity in measuring the effects of social care services than EQ-5D. Van Leeuwen et al. [ 28] investigated the validity of ICECAP-O and ASCOT among Dutch older adults. Although it could be attributable to cultural transferability issues, they found that respondents did not feel that these instruments give a comprehensive picture of their HRQoL because they did not find all domains of the instruments relevant, whilst other important domains were not covered, particularly concerns or delight about the well-being of family members. HRQoL instruments capture an important part of broader well-being, and some studies [ 22, 23] established strong and positive association between capability and HRQoL instruments, which questions whether they focus on complementary constructs. Evidence suggests that some capability instruments could rather be interpreted as an enhancement of the HRQoL concept, for instance, an exploratory factor analysis [ 17] found that all EQ-5D-5L items and seven OxCAP-MH items loaded on one factor and nine remaining OxCAP-MH items loaded on a separate factor.
It is questionable whether the issues discussed above relate to all HRQoL measures or only the EQ-5D Utility instrument. Lower correlation between the OxCAP-MH and EQ-5D Utility scores was observed in the Vergunst et al. [ 19] study than between OxCAP-MH and EQ-5D-VAS. This could be explained by the fact that the latter reflects the patient’s overall judgement about their health status rather than focusing only five dimensions of their health, which is arguably more in line with the underlying broader well-being concept and the used non-preference-based index score of the OxCAP-MH instrument.
Interpretability
In terms of ease of understanding, Bailey et al. [ 29] investigated the appropriateness of ICECAP-SCM to measure QoL and found that the capability instrument appeared more meaningful, easier to complete and had fewer errors among patients and close persons, compared to EQ-5D-5L. However, these results did not apply to healthcare professionals who preferred the EQ-5D-5L over ICECAP-SCM when measuring clinician-rated health states because it focused on observable attributes. Similar studies have also demonstrated the feasibility of use of other ICECAP measures [ 81, 90]. Malley et al. [ 70] and Towers et al. [ 67] demonstrated the feasibility of using ASCOT among older people and care home residents; however, the study also highlighted the need for proxy respondents in some situations. This later led to the development of a proxy version of the ASCOT, which demonstrated good feasibility [ 58]. Davis et al. [ 30] reported that the level of agreement between patient and proxy for the EQ-5D-3L was significantly better than the level of agreement observed for the ICECAP-O in case of patients with vascular cognitive impairment. The authors conclude that due to its complexity, the ICECAP-O may have limited clinical, research and policy-related utility among individuals with mild cognitive impairment. However, these results need to be interpreted carefully due to the differing number of levels and the greater ability of proxies to observe the dimensions in EQ-5D. Although it could be explained by translational issues, van Leeuwen [ 28] who also reported difficulties with understanding the ASCOT and ICECAP-O in a study assessing a small number ( n = 10) of Dutch, community-dwelling frail older adults. Simon et al. [ 39] explored the feasibility of OxCAP-MH among severely ill mental health service users. Patients provided positive feedback and felt that the questions allowed them to express their views and experience on topics they considered important but which were often left out of clinical or research interviews [ 39].
Responsiveness
The sensitivity of the capability instruments to measure changes is generally reported to be higher than in case of HRQoL measures [ 6, 17, 3134]. However, some authors found capability instruments to be less responsive than HRQoL measures. Davis et al. [ 35] and Couzner et al. [ 36] reported that the difference in values between the patient and general population groups was found to be far more pronounced for the EQ-5D-3L than for the ICECAP-O. There is a consensus in the literature that changes related to the broader meaning of health are better captured by the capability instruments than by EQ-5D [ 3739]. Coast et al. [ 40] found strong evidence of association of general health with all capability attributes except for the attachment domain of ICECAP-A. Laszewska et al. [ 17] found that the OxCAP-MH may be seen as enhanced rather than complementary in its concept, when compared to EQ-5D-5L.

Valuation of instruments

From the reviewed 14 capability instruments, only four have a published valuation set. These used the best–worst scaling method, most often relying on the MaxDiff model. Informants mainly came from the general public. There is no published evidence available for the valuation of the remaining ten capability questionnaires (Table  6).
Table 6
Valuation of capability instruments for health economic evaluations
Instrument
Methods of valuation
Number of choices per BWS task
Number of BWS tasks per respondents
Population
Number of informants
References
ASCOT
BWS, TTO
4
8
General public
958 (BWS) + 126 (TTO)
[ 52]
ICECAP-A
BWS
5
16
General public
413
[ 85]
ICECAP-O
Variants of DCEs and BWS tasks (online)
5
16
General public aged 65 or over
255
[ 88]
ICECAP-SCM
BWS
7
16
General public
6020
[ 101, 110]

Applied economic evaluations and potential methods to incorporate the capability approach

Ten applied evaluations were identified in this review that have used a capability-based instrument as secondary outcome measure in health economic evaluations. No economic evaluation was found where a capability instrument was used as a primary measure of health outcomes. The information extracted from the applied evaluations is presented in Table  7 and in Appendix 6.
Table 7
Applied evaluations using the capability approach in their economic evaluations
Capability measure
Disease
Time points
Other HE measures
Changes in QALYs vs. capability values
Presentation of results
Reference
ICECAP-A
Visual impairment
Baseline; 2–4 months
EQ-5D-5L
Nearly identical a
Cost per Year of Full Capability (YFC)
[ 111]
Diabetic plantar ulceration
Baseline; 6 months
EQ-5D-5L
QALYs negative; Capability positive
Cost and outcome data presented separately
[ 43]
Drug addiction
Baseline; 12 months
EQ-5D-5L
Full capability higher than Sufficient capability, and both higher than QALYs
Years of full capability (YFC), years of sufficient capability equivalent (YSC)
[ 112]
Schizophrenia
Baseline; 12–36–48 weeks
EQ-5D-3L
Nearly identical a
Cost and outcome data presented separately
[ 44]
ICECAP-O
Health decline in the older people
Baseline; 3 months
EQ-5D-3L
QALYs positive; Capability negative
Incremental net monetary benefit (INMB) regressions based on capability QALYs
[ 31]
Heart failure, chronic obstructive pulmonary disease, or diabetes
Baseline; 12 months
EQ-5D-3L
Nearly identical a
Willingness to pay for 100% improvement in capability
[ 113]
Visual impairment
3 months; post-intervention; pre-study
EQ-5D-5L
Capability higher than QALYs
Costs per years of well-being
[ 46]
Hip fracture
Baseline; 3 months
EQ-5D-3L
Capability lower than QALYs
Cost and outcome data presented separately
[ 42]
OxCAP-MH
Psychosis
Baseline; 6–12 months
EQ-5D-3L
Nearly identical a
Cost and outcome data presented separately
[ 45]
ICECAP-A and OxCAP-MH
Schizophrenia or schizoaffective disorder and depression
Baseline, 3–6–9 months
EQ-5D-5L
QALYs positive; Capability: no significant change
Cost and outcome data presented separately
[ 114]
aNearly identical means that the difference between baseline and follow-up are within a 10% range when comparing the QALYs and capability estimates
The number of economic evaluations reporting the use of a capability instrument has increased in recent years and further increases can be expected given that this search identified a number of recent study protocols (e.g. [ 41, 42, 114]). Four further studies were identified that specifically addressed the issues and discussed considerations when incorporating the capability approach into health-related economic evaluations.
A recent review [ 13] focused on using the capability approach in health research, not limited to economic evaluations. It identified four distinct common areas of application including: (1) physical activity and diet; (2) patient empowerment; (3) multidimensional poverty and (4) assessments of health and social care interventions. The authors also noted that there is a noticeable non-reliance on health status as a sole indicator of capability in health, and differences were found across studies in approaches to applying mixed methods, selecting capability dimensions and weighting capabilities. The current review identified applied economic evaluations from areas with widely accepted issues related to outcomes beyond the QALYs framework, e.g. mental health, visual impairment, chronic diseases and health decline in older people.
The presentation of results in the included economic evaluations demonstrate that there is a lack of consensus regarding the most appropriate way to use capability instruments in economic evaluations. Some authors present cost and outcome data separately and conduct a cost-consequence analysis [ 4245], whilst others reported the results following the idea behind the incremental cost-effectiveness ratio (ICER) [ 31, 46]. This lack of consensus about the use of capability instruments in decision making relates to the different approaches taken by different research groups to valuation, which means that in practice these measures are not comparable along the lines of a QALY. The idea of CALYs has been proposed by Mansdotter et al. [ 47] who highlights the following issues. First, it is questionable which capabilities are able to explain differences in well-being and are sensitive to public policies in high-income countries. Second, questions of the relevant instruments should capture voluntary and involuntary positions because an applied conceptualization of the capability approach includes opportunity as well as achievement. Third, methods for weighting capability and threshold values should be established, similar to QALYs. Finally, a trade-off should be made between the maximisation of capability and equity.
Mitchell et al. [ 48] proposed the concept of years of sufficient capability which is more closely aligned to the theory underpinning the capability approach because it has a greater focus on those in capability poverty. The process of defining a threshold for sufficient capability should be based on generating a sufficient capability score and using these scores to produce a capability outcome over time [ 48]. The use of ICECAP-A in the economic evaluations included in this literature review seem to focus on the choice between the options of years of full capability vs. years of sufficient capability equivalent [ 48].
The current state of the art identified in the reported economic evaluations applying the capability approach to their assessment are in line with the previously identified main challenges [ 50], including the need to research what the value of a capability improvement is, how to use the instruments globally, and compare the sensitivity of each measure to different patient groups and conditions. Only one study [ 49] was identified that posed a critique to using the capability approach in health economic evaluations. The authors claim that the method used in the questionnaires to measure capability will result in a capability set that is an inaccurate description of the individual’s true capability set. The measured capability set will either represent only one combination and ignore the value of choice in the capability set, or represent one combination that is not actually achievable by the individual. In addition, existing methods of valuing capability may be inadequate because they do not consider that capability is a set. (Although the Oxford instruments were developed based on Nussbaum’s 10 basic human capabilities.) Hence, it may be practically more feasible to measure and value capability approximately rather than directly. Nevertheless, the argument is based on the questionable assumption that all capabilities have to be traded against other capabilities.

Discussion

This systematic literature review about capability instruments in economic evaluations of health-related interventions included 98 articles and identified 14 capability-based instruments. It provides a unique, comprehensive synthesis of the relevant evidence by focusing on the full spectrum of potentially available capability measures and summarising the practical and theoretical aspects of use of these instruments in economic evaluations. Most identified information related to the ASCOT, ICECAP-A, ICECAP-O and OxCAP-MH instruments.
The development of capability instruments relies on methods similar to those applied in the case of HRQoL measures. Capability instruments were often compared to EQ-5D, but less often to each other. Possible reasons for this are that some instruments are population or disease-specific, and that the inclusion of two instruments measuring the same concept in an applied evaluation study is assumed to unnecessarily increase participants’ completion burden. In general, the information identified in the literature regarding the comparison of capability measures with other instruments could not be used for a pooled analysis. This is mainly due to the vast variation in the correlation measures used, the instruments compared, the characteristics of the populations and the number of informants. Despite the diverse quantitative estimates for the correlations with EQ-5D, the different capability instruments and the limited available data, this review confirms that capability measures capture a wider range of outcomes than the EQ-5D and may be more responsive when an intervention is likely to have broad impacts on HRQoL. Following the guidelines [ 51] to evaluate the strength of correlations, this generally observed moderate-to-high correlation suggests that EQ-5D and capability instruments measure somewhat similar, yet complementary concepts. However, there are competing statements in the literature regarding the association between capability and HRQoL instruments. Most authors argue that these measures complement each other; however, some studies suggest that capability instruments could be perceived as enhancements of the HRQoL concept. It is possible that this relationship depends on the choice of both capability and health instruments used in these comparisons. For instance, the OxCAP-MH has a relatively high number of items, which potentially capture a broader range of capability concepts than measures such as the ICECAP measures. Similarly, the EQ-5D measure of health has a narrower focus than other health measures such as measures based on SF-36 or the AQoL. The higher correlations between capability instruments and the EQ-5D-VAS scores than those observed between capability instruments and the EQ-5D utility scores suggest that respondents’ overall judgement of their health status on a VAS seems to reflect better broader quality-of-life concepts present in the capability approach than specific scores for a certain limited number of HRQoL dimensions. Moreover, the differences in correlations found between measures may be due to differences in the populations studied. Hence, further research could explore which population subgroups and disease areas could benefit from the inclusion of certain capability instruments in economic evaluations.
Three of the identified 14 capability instruments were used in applied economic evaluation of interventions in the health and social care field; however, only as secondary outcome measures. Eight of the identified ten applied economic evaluations were conducted in the United Kingdom. This may be the result of the fact that the measures were developed in the UK and only available in English for some years. From the perspective of (health) economists concerned with economic evaluations, a good outcome measure should possess three main characteristics [ 2]. First, it should be comparable among diseases and interventions to allow for interpretation in a comparative way for resource allocation purposes. The capability instruments identified in this literature review were developed for specific population groups; hence, a comparison is currently challenging without a standard application of, for instance, the CALYs framework. Second, the instruments should have a scale with interval properties. All instruments provide a summary score; however, only a few are anchored and therefore have interval properties. The ICECAP scores are anchored on no capability and full capability, and the ASCOT scales are anchored on death and full capability. Finally, most economists are looking for an outcome measure for economic evaluation that reflects preferences, either of individual patients or the general public. Instruments with tariffs derived from the general population (ASCOT, ICECAP-A and ICECAP-SCM) or the relevant subpopulation (ICECAP-O) possess this characteristic. On the other hand, reducing capabilities information only to a single, preference-based index value on a scale of 0–1 may limit the actionable policy relevance of the information [ 39]. The two approaches, however, are not mutually exclusive and more research is needed about the relative values of different capabilities and their variance according to population specifics (e.g. age, disease experience, culture). More information about the weights people allocate to the attributes and levels of capability instruments would be needed to improve our understanding of the relative value of individual capability domains and dimensions.
Major limitations of this study design include that the search was limited to English and German. Next, this review only assessed instruments and studies reported in the literature, and a thorough grey literature search could not be conducted due to difficulties with the search term capability. In terms of grey literature, only dedicated websites of capability instruments were reviewed for relevant information. This resulted in some limitations, for instance, some cost-effectiveness components of studies that have used ASCOT have not been written up as journal articles and fell therefore outside the findings of this review [ 118, 119]. Furthermore, ongoing research and developments could not be included which could be important in such a dynamically moving area. For example, we found information about ongoing economic evaluations [ 41, 42, 114] with the identified instruments where results expected to be published soon, additional capability instruments might have been used in unpublished economic evaluations, or some are currently under development. There is a potential need to update this literature review in the future to gather information from this rapidly growing body of literature about the potential development of additional capability measures, the further validation of existing ones, the empirical use of capability measures in economic evaluations, and the lessons learned from these applications.

Conclusion

There has been an increasing interest in the application of the capability-based approach in economic evaluations of health-related interventions. Different instruments are available and the choice between them should be based on both the research question and the characteristics of the instruments. Further research should focus on the comparison of the existing capability instruments and examining the correlation across capability measures. This would help future researchers in choosing the most suitable capability instrument for their study and provide further information for instrument developers.

Acknowledgements

Open access funding provided by Medical University of Vienna.

Compliance with ethical standards

Conflict of interest

JC has led the development of the ICECAP measures. JS has led the development of the OxCAP-MH measure. The remaining authors declare that they have no conflict of interest.
Open AccessThis article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://​creativecommons.​org/​licenses/​by/​4.​0/​

Appendix 1: search strategy

Embase and Medline via Embase.com

((‘economic evaluation’/exp OR ‘economic*’:ti,ab,kw OR ‘cost-effective*’:ti,ab,kw OR ‘cost-utility’:ti,ab,kw OR ‘cost-benefit’:ti,ab,kw) AND ((‘ascot’:ti,ab,kw OR ‘icecap’:ti,ab,kw OR ‘oxcap-mh’:ti,ab,kw) OR (capabilit* NEXT/2 (perspective OR approach)):ti,ab,kw)) AND (2000:py OR 2001:py OR 2002:py OR 2003:py OR 2004:py OR 2005:py OR 2006:py OR 2007:py OR 2008:py OR 2009:py OR 2010:py OR 2011:py OR 2012:py OR 2013:py OR 2014:py OR 2015:py OR 2016:py OR 2017:py OR 2018:py OR 2019:py) ( 182 results ).

Web of science

TS = (“economic evaluation”) OR TI = (“economic evaluation”) OR TS = (“economic assessment”) OR TI = (“economic assessment”) OR TS = (cost-effectiveness) OR TI = (cost-effectiveness) OR TS = (cost-utility) OR TI = (cost-utility) OR TS = (cost-benefit) OR TI = (cost-benefit) AND TS = (“capabilit* approach”) OR TI = (“capabilit* approach”) OR TS = (“capabilit* perspective”) OR TI = (“capabilit* perspective”) OR TS = (ascot) OR TI = (ascot) OR TS = (icecap*) OR TI = (icecap*) OR TS = (oxcap-mh) OR TI = (oxcap-mh)
Limitations: Last 20 years
Indexes = SCI-EXPANDED, SSCI, A&HCI, CPCI-S, CPCI-SSH, ESCI ( 90 results)

Psychinfo

((capabilit* or ascot or oxcap-mh or icecap).ab. or (capabilit* or ascot or oxcap-mh or icecap).ti.) and ((cost-effectiveness or cost-utility or cost-benefit or economic evaluation or economic assessment).ti. or (cost-effectiveness or cost-utility or cost-benefit or economic evaluation or economic assessment).ab.)
Limitations: Last 20 years ( 82 results)

Scopus

TITLE-ABS-KEY ((“capabilit* approach”) OR (“capabilit* perspective”) OR (ascot) OR (oxcap-mh) OR (icecap)) AND TITLE-ABS-KEY ((economic AND evaluation) OR (economic AND assessment) OR cost-effectiveness OR cost-utility OR cost-benefit)
Limitations: English, German, last 20 years ( 174 results)

Appendix 2: data extraction

The final list of extracted data in case of applied papers included
  • First author,
  • Year of publication (1999, …, 2018),
  • Country of study, Disease area,
  • Type of intervention,
  • Population under investigation,
  • Aim of study (to assess cost-effectiveness, to …),
  • Type of economic evaluation (cost-minimisation analysis, cost-consequence analysis, cost-effectiveness analysis, cost-utility analysis, cost–benefit analysis, not applicable),
  • Perspective of study (healthcare service, societal, other),
  • Capability instrument used (multiple choice between: ICECAP-A, ICECAP-O, OxCAP-MH, ASCOT, Other),
  • Time points of measurement (pre-study, baseline, post-study, 1 month, …, 12 months, beyond 12 months),
  • Other instruments used,
  • Methods to address missing data,
  • Presentation of results, e.g. cost/CALYs, p value of capability instrument (less than 0.05, greater than 0.05), Comparison of results to QALYs (lower, nearly identical, higher),
  • Comparison of incremental cost-effectiveness ratios (difference in costs per extra year to gain well-being, expressed in EUR),
  • Use of capability data in economic modelling (yes, no),
  • Recommendation to apply capability in future economic evaluations (yes, no),
  • Further comments on the capability instrument.
Data extraction in case of methods papers included the
  • First author,
  • Year of publication (2009, …, 2018),
  • Type of study (Comparison of questionnaires; Development of questionnaires; Methods to incorporate CA to economic evaluation; Theoretical background of CA),
  • Aim of study,
  • Capability instrument in question (multiple choice between: ICECAP-A, ICECAP-O, OxCAP-MH, ASCOT, Other),
  • Recommendation to apply capability in future economic evaluations (yes, no),
  • Further comments on the capability instrument.

Appendix 3

See Table  8.
Table 8
List of included papers
Author
Year
References
Category
Instrument(s)
Al-Janabi
2012
[ 53]
Development
ICECAP-A
Al-Janabi
2015
[ 77]
Validation
ICECAP-A
Al-Janabi
2013
[ 33]
Validation
ICECAP-A
Al-Janabi
2013
[ 82]
Validation
ICECAP-A
Bailey
2016
[ 29]
Validation
ICECAP-SCM
Barnes
2016
[ 44]
Empirical
ICECAP-A
Baumgardt
2018
[ 103]
Validation
OxCAP-MH
Botes
2018
[ 60]
Development
CAF
Botes
2018
[ 115]
Validation
CAF
Bray
2017
[ 111]
Empirical
ICECAP-A
Burns
2016
[ 45]
Empirical
OxCAP-MH
Chen
2018
[ 20]
Validation
ICECAP-A
Coast
2008
[ 88]
Valuation
ICECAP-O
Coast
2016
[ 100]
Valuation
ICECAP-SCM
Coast
2008
[ 40]
Validation
ICECAP-O
Coast
2018
[ 83]
Validation
ICECAP-A, ICECAP-SCM
Comans
2012
[ 97]
Validation
ICECAP-O
Couzner
2012
[ 22]
Comparison
ICECAP-O
Couzner
2013
[ 36]
Validation
ICECAP-O
Davis
2013
[ 25]
Comparison
ICECAP-O
Davis
2016
[ 30]
Validation
ICECAP-O
Davis
2017
[ 35]
Validation
ICECAP-O
Engel
2018
[ 78]
Validation
ICECAP-A
Engel
2018
[ 79]
Validation
ICECAP-A
Engel
2016
[ 89]
Validation
ICECAP-O
Engel
2017
[ 24]
Comparison
ICECAP-A
Flynn
2015
[ 85]
Valuation
ICECAP-A
Forder
2011
[ 68]
Validation
ASCOT
Franklin
2018
[ 26]
Comparison
ICECAP-O
Goranitis
2016
[ 34]
Comparison
ICECAP-A
Goranitis
2017
[ 112]
Empirical
ICECAP-A
Goranitis
2016
[ 23]
Validation
ICECAP-A
Greco
2018
[ 102]
Validation
low-income Q
Greco
2015
[ 64]
Development
low-income Q
Grewal
2006
[ 54]
Development
ICECAP-O
Hackert
2017
[ 21]
Comparison
ASCOT, ICECAP-O
Hackert
2019
[ 90]
Validation
ICECAP-O
Handels
2018
[ 109]
Translation
ICECAP-O
Henderson
2013
[ 113]
Empirical
ICECAP-O
Horder
2016
[ 86]
Validation
ICECAP-O
Horwood
2014
[ 91]
Validation
ICECAP-O
Huynh
2017
[ 101]
Valuation
ICECAP-SCM
Jones
2017
[ 32]
Validation
ICECAP-A
Kaambwa
2019
[ 69]
Validation
ASCOT
Karimi
2016
[ 49]
Incorporation
General
Keeley
2013
[ 80]
Validation
ICECAP-A
Keeley
2015
[ 81]
Validation
ICECAP-A
Keeley
2016
[ 27]
Comparison
ICECAP-A
Khan
2018
[ 116]
Validation
ICECAP-A
Kinghorn
2015
[ 65]
Development
Pain Q
Łaszewska
2019
[ 17]
Comparison
OxCAP-MH
Linton
2018
[ 108]
Validation
ICECAP-A
Looman
2014
[ 98]
Validation
ICECAP-O
Lorgelly
2015
[ 63]
Development
OCAP-18
Makai
2014
[ 6]
Validation
ASCOT, ICECAP-O
Makai
2015
[ 31]
Empirical
ICECAP-O
Makai
2012
[ 92]
Validation
ICECAP-O
Makai
2014
[ 18]
Validation
ICECAP-O
Malley
2012
[ 70]
Validation
ASCOT
Mansdotter
2017
[ 47]
Incorporation
General
Milte
2014
[ 71]
Comparison
ASCOT
Milte
2018
[ 93]
Validation
ICECAP-O
Mitchell
2017
[ 13]
Incorporation
General
Mitchell
2015
[ 37]
Validation
ICECAP-A
Mitchell
2013
[ 94]
Comparison
ICECAP-O
Mitchell
2015
[ 48]
Incorporation
General
Mitchell
2017
[ 38]
Comparison
ICECAP-A
Netten
2012
[ 52]
Development
ASCOT
Parker
2019
[ 43]
Empirical
ICECAP-A
Parsons
2014
[ 95]
Validation
ICECAP-O
Patty
2018
[ 46]
Empirical
ICECAP-O
Peak
2018
[ 84]
Validation
ICECAP-A
Rand
2017
[ 72]
Comparison
ASCOT
Rand
2012
[ 58]
Development
ASCOT-proxy
Ratcliffe
2013
[ 99]
Validation
ICECAP-O
Sacchetto
2016
[ 56]
Development
ACQ‐CMH‐104
Sacchetto
2018
[ 66]
Validation
ACQ‐CMH‐104
Sarabia-Cobo
2017
[ 87]
Comparison
ICECAP-O
Shiroiwa
2018
[ 105]
Validation
ASCOT
Simon
Unpublished
[ 114]
Empirical
OxCAP-MH
Simon
2018
[ 117]
Translation
OxCAP-MH
Simon
2013
[ 39]
Development
OxCAP-MH
Stevens
2018
[ 73]
Comparison
ASCOT
Sutton
2014
[ 62]
Development
ICECAP-SCM
Tang
2018
[ 107]
Comparison
ICECAP-A
Towers
2015
[ 75]
Validation
ASCOT
Towers
2016
[ 67]
Validation
ASCOT
Turnpenny
2018
[ 57]
Development
ASCOT Easy Read
Van Leeuwen
2015
[ 74]
Comparison
ASCOT, ICECAP-O
Van Leeuwen
2015
[ 106]
Validation
ASCOT
Van Leeuwen
2014
[ 104]
Validation
ASCOT
Van Leeuwen
2015
[ 28]
Validation
ASCOT, ICECAP-O
Vergunst
2017
[ 19]
Comparison
OxCAP-MH
Williams
2016
[ 42]
Empirical
ICECAP-O
Xin
2017
[ 96]
Comparison
ICECAP-O

Appendix 4

See Table  9.
Table 9
Correlations reported in the included studies
Capabilities instrument
Compared with (long name)
Compared with (short name)
Country
Population
Number of informants
Measurement of correlation
Value of correlation
Reference
ACQ‐CMH‐104
WHOQOL‐Bref
WHOQOL‐Bref
Portugal
Psychiatric patients participating in community mental health organisations
129
Pearson coefficient
0.60
[ 66]
ACQ‐CMH‐104
RAS-P
Recovery assessment scale
Portugal
Psychiatric patients participating in community mental health organisations
92
Pearson coefficient
0.46
[ 66]
ASCOT
EQ-5D-3L
EQ-5D-3L
UK
Day care for older people
224
Spearman Rank
0.47
[ 68]
ASCOT
ICECAP-O
ICECAP-O
UK
Older social care users
205
Spearman Rank
0.81
[ 21]
ASCOT
EQ-5D-5L
EQ-5D-5L
UK
Older social care users
205
Spearman Rank
0.63
[ 21]
ASCOT
EQ-5D-VAS
EQ-5D-VAS
UK
Older social care users
205
Spearman Rank
0.64
[ 21]
ASCOT
Barthel Index
Barthel Index
UK
Older social care users
205
Spearman Rank
0.45
[ 21]
ASCOT
GDS-15 (negative correlation)
GDS-15*
UK
Older social care users
205
Spearman Rank
0.69
[ 21]
ASCOT
OPQOL-13
OPQOL-13
UK
Older social care users
205
Spearman Rank
0.76
[ 21]
ASCOT
SWLS
SWLS
UK
Older social care users
205
Spearman Rank
0.74
[ 21]
ASCOT
Cantril’s Ladder
Cantril’s Ladder
UK
Older social care users
205
Spearman Rank
0.66
[ 21]
ASCOT
Older People’s Quality-of-Life brief questionnaire
OPQoL-Brief
Australia
Community-dwelling older people receiving aged care services
87
Spearman Rank
0.58
[ 69]
ASCOT
EQ-5D-3L
EQ-5D-3L
UK
Older people receiving publicly funded home care services
301
Pearson correlation
0.40
[ 70]
ASCOT
EQ-5D-5L
EQ-5D-5L
Australia
Older adults in a day rehabilitation facility
22
Spearman Rank
0.24
[ 71]
ASCOT
Brief Older People’s Quality of Life
OPQOL-brief
Australia
Older adults in a day rehabilitation facility
22
Spearman Rank
0.38
[ 71]
ASCOT
EQ-5D-3L
EQ-5D-3L
UK
Older home care residents
301
Pearson coefficient
0.41
[ 52]
ASCOT
GHQ-12 (negative correlation)
GHQ-12*
UK
Older home care residents
301
Pearson coefficient
0.58
[ 52]
ASCOT
Control and autonomy subscale of CASP-12
CASP-12
UK
Older home care residents
301
Pearson coefficient
0.58
[ 52]
ASCOT
EQ-5D-3L
EQ-5D-3L
UK
General population
200
Gradient
0.98
[ 73]
ASCOT
EQ-5D-3L
EQ-5D-3L
Netherlands
Frail older adults living at home
190
Spearman Rank
0.41
[ 74]
ASCOT
ICECAP-O
ICECAP-O
Netherlands
Frail older adults living at home
190
Spearman Rank
0.41
[ 74]
ASCOT
EQ-5D-3L
EQ-5D-3L
UK
Community-based adult social care service users
748
Spearman Rank
0.37
[ 72]
ASCOT
ICECAP-O
ICECAP-O
UK
Community-based adult social care service users
748
Spearman Rank
0.67
[ 72]
ASCOT
ICECAP-A
ICECAP-A
UK
Community-based adult social care service users
748
Spearman Rank
0.62
[ 72]
ASCOT-Carer
Carer Experience Scale (CES)
CES
UK
Social care recipients
376
Spearman Rank
0.58
[ 76]
ASCOT-Carer
Carer Strain Index (negative correlation)
CSI
UK
Social care recipients
384
Spearman Rank
− 59
[ 76]
ASCOT-Carer
EQ-5D-3L
EQ-5D-3L
UK
Social care recipients
382
Spearman Rank
0.34
[ 76]
ASCOT-Carer
QoL (single item using a 7-point Likert scale)
QoL
UK
Social care recipients
384
Spearman Rank
0.62
[ 76]
ICECAP-A
Assessment of Quality of Life
AQoL-8D
Australia, Canada, Germany, Norway, UK, USA
Patients with seven chronic conditions and a sample of the ‘healthy’ public
8022
Spearman Rank
0.80
[ 20]
ICECAP-A
EQ-5D-5L
EQ-5D-5L
Australia, Canada, Germany, Norway, UK, USA
Patients with seven chronic conditions and a sample of the ‘healthy’ public
8022
Spearman Rank
0.60
[ 20]
ICECAP-A
15D
15D
6 countries (MIC)
Representative healthy cohort and from patients in eight clinical areas
6756
Pearson coefficient (average of correlations among factors)
0.50
[ 24]
ICECAP-A
AQoL-8D
AQoL-8D
6 countries (MIC)
Representative healthy cohort and from patients in eight clinical areas
6756
Pearson coefficient (average of correlations among factors)
0.31
[ 24]
ICECAP-A
EQ-5D-5L
EQ-5D-5L
6 countries (MIC)
Representative healthy cohort and from patients in eight clinical areas
6756
Pearson coefficient (average of correlations among factors)
0.49
[ 24]
ICECAP-A
HUI-3
HUI-3
6 countries (MIC)
Representative healthy cohort and from patients in eight clinical areas
6756
Pearson coefficient (average of correlations among factors)
0.32
[ 24]
ICECAP-A
SF-6D
SF-6D
6 countries (MIC)
Representative healthy cohort and from patients in eight clinical areas
6756
Pearson coefficient (average of correlations among factors)
0.47
[ 24]
ICECAP-A
HUI-3
HUI-3
Australia, Canada, Germany, Norway, UK, and USA
Individuals with self-reported depression
917
R 2
0.46
[ 79]
ICECAP-A
SF-6D
SF-6D
Australia, Canada, Germany, Norway, UK, and USA
Individuals with self-reported depression
917
R 2
0.36
[ 79]
ICECAP-A
15D
15D
Australia, Canada, Germany, Norway, UK, and USA
Individuals with self-reported depression
917
R 2
0.42
[ 79]
ICECAP-A
Assessment of Quality-of-Life Multi-Attribute Utility Instrument
AQoL-8D
Australia, Canada, Germany, Norway, UK, and USA
Individuals with self-reported depression
917
R 2
0.58
[ 79]
ICECAP-A
EQ-5D-5L
EQ-5D-5L
Australia, Canada, Germany, Norway, UK, and USA
Individuals with self-reported depression
917
R 2
0.34
[ 79]
ICECAP-A
EQ-5D-5L
EQ-5D-5L
Canada
Patients with Spinal Cord Injury
364
Path analysis
0.37
[ 78]
ICECAP-A
Assessment of Quality-of-Life Multi-Attribute Utility Instrument
AQoL-8D
Canada
Patients with Spinal Cord Injury
364
Path analysis
0.54
[ 78]
ICECAP-A
Leeds Dependence Questionnaire (negative correlation)
LDQ*
UK
Individuals receiving opiate substitution treatment for more than 12 months
83
Pearson coefficient
0.48
[ 34]
ICECAP-A
Social Satisfaction Questionnaire
SSQ
UK
Individuals receiving opiate substitution treatment for more than 12 months
83
Pearson coefficient
0.43
[ 34]
ICECAP-A
EQ-5D-3L
EQ-5D-3L
UK
Women with lower urinary tract symptoms
478
Pearson coefficient
0.53
[ 23]
ICECAP-A
EQ-5D-3L
EQ-5D-3L
UK
Knee pain patients in primary care
500
Spearman Rank
0.49
[ 27]
ICECAP-A
36-Item Short Form Health Survey
SF-36
Australia, Canada, Germany, Norway, UK, USA
Patients with seven chronic conditions and a sample of the ‘healthy’ public
8022
R 2
0.57
[ 116]
ICECAP-A
36-Item Short Form Health Survey
AQoL-8D
Australia, Canada, Germany, Norway, UK, USA
Patients with seven chronic conditions and a sample of the ‘healthy’ public
8022
R 2
0.71
[ 116]
ICECAP-A
EQ-5D-5L
EQ-5D-5L
Germany
Healthy Samples and Seven Health Condition Groups
1212
Pearson coefficient
0.62
[ 108]
ICECAP-A
SWLS
SWLS
Germany
Healthy Samples and Seven Health Condition Groups
1212
Pearson coefficient
0.66
[ 108]
ICECAP-A
SF-6D
SF-6D
Germany
Healthy Samples and Seven Health Condition Groups
1212
Pearson coefficient
0.64
[ 108]
ICECAP-A
Depression, Anxiety and Stress Scale
DASS-D
4 English speaking countries of MIC
Individuals with depression
617
R 2
?
[ 38]
ICECAP-A
Kessler Psychological Distress Scale
K10
4 English speaking countries of MIC
Individuals with depression
617
R 2
?
[ 38]
ICECAP-A
EQ-5D-3L
EQ-5D-3L
China
General population
975
Polychoric correlation coefficient
0.45
[ 107]
ICECAP-O
EQ-5D-3L
EQ-5D-3L
UK
General population aged 65 and over
315
Chi-squared tests
0.42 (Attachment), 0.008** (Security), < 0.001** (Role), < 0.001** (Enjoyment), < 0.001** (Control)
[ 40]
ICECAP-O
EQ-5D
EQ-5D-3L
Australia
Patients from an outpatient day rehabilitation unit
80
Spearman Rank
0.44
[ 22]
ICECAP-O
CTM-3
CTM-3
Australia
Patients from an outpatient day rehabilitation unit
82
Spearman Rank
0.23
[ 22]
ICECAP-O
EQ-5D
EQ-5D-3L
Canada
Participants visiting the Vancouver Falls Prevention Clinic
215
Spearman Rank
0.47
[ 25]
ICECAP-O
EQ-5D-3L
EQ-5D-3L
UK
Aged over 65 years, requiring a hospital visit and/or care home resident, and recruited to one of 3 studies forming the Medical Crisis in Older People (MCOP) programme
584
R 2
0.35
[ 26]
ICECAP-O
EQ-5D-5L
EQ-5D-5L
UK
Older social care users
207
Spearman Rank
0.68
[ 21]
ICECAP-O
EQ-5D-VAS
EQ-5D-VAS
UK
Older social care users
208
Spearman Rank
0.66
[ 21]
ICECAP-O
Barthel Index
Barthel Index
UK
Older social care users
209
Spearman Rank
0.49
[ 21]
ICECAP-O
GDS-15 (negative correlation)
GDS-15*
UK
Older social care users
210
Spearman Rank
0.73
[ 21]
ICECAP-O
OPQOL-13
OPQOL-13
UK
Older social care users
211
Spearman Rank
0.80
[ 21]
ICECAP-O
SWLS
SWLS
UK
Older social care users
212
Spearman Rank
0.82
[ 21]
ICECAP-O
Cantril’s Ladder
Cantril’s Ladder
UK
Older social care users
213
Spearman Rank
0.74
[ 21]
ICECAP-O
EQ-5D-5L
EQ-5D-5L
UK
People aged 70 and older
516
Spearman Rank
0.63
[ 90]
ICECAP-O
Barthel Index
Barthel Index
Germany
Nursing Home Residents with Dementia
95
Pearson coefficient
0.72
[ 18]
ICECAP-O
EQ-5D-3L
EQ-5D-3L
Germany
Nursing Home Residents with Dementia
95
Pearson coefficient
0.69
[ 18]
ICECAP-O
ADRQL
ADRQL
Germany
Nursing Home Residents with Dementia
95
Pearson coefficient
0.53
[ 18]
ICECAP-O
EQ-5D-3L
EQ-5D-3L
Australia
Older people following surgery for hip fracture
87
Spearman Rank
0.53
[ 93]
ICECAP-O
Western Ontario and McMaster Universities
WOMAC
UK
Osteoarthritis patients requiring joint replacement
105
R 2
0.40
[ 94]
ICECAP-O
EQ-5D-3L
EQ-5D-3L
UK
Participants aged 65 years and over with an intracapsular fracture of the hip
113
Pearson coefficient
0.34
[ 95]
ICECAP-O
Oxford Hip Score
OHS
UK
Participants aged 65 years and over with an intracapsular fracture of the hip
113
Pearson coefficient
0.38
[ 95]
ICECAP-O
Barthel Index measure of activities of daily living
Barthel Index
Spain
Nursing professionals serving as proxy respondents for dementia patients
217
Not reported
0.68
[ 87]
ICECAP-O
Alzheimer’s Disease-Related Quality of Life
ADRQL
Spain
Nursing professionals serving as proxy respondents for dementia patients
217
Not reported
0.61
[ 87]
ICECAP-O
EQ-5D extended with a cognitive dimension
EQ-5D + C
Spain
Nursing professionals serving as proxy respondents for dementia patients
217
Not reported
0.62
[ 87]
ICECAP-O
EQ-5D-3L
EQ-5D-3L
Netherlands
Frail older adults living at home
190
Spearman Rank
0.63
[ 74]
ICECAP-O
Parkinson’s specific QoL
PDQ-39
?
People with Parkinson’s
1023
Not reported
0.53
[ 96]
ICECAP-O family version
EQ-5D family version
EQ-5D family version
Netherlands
Nursing professionals of psycho-geriatric elderly
96
Pearson coefficient
0.57
[ 92]
ICECAP-O family version
EQ-VAS family version
EQ-VAS family version
Netherlands
Family members of psycho-geriatric elderly
68
Pearson coefficient
0.43
[ 92]
ICECAP-O nursing version
EQ-5D nursing version
EQ-5D nursing version
Netherlands
Nursing professionals of psycho-geriatric elderly
96
Pearson coefficient
0.48
[ 92]
ICECAP-O nursing version
EQ-VAS nursing version
EQ-VAS nursing version
Netherlands
Family members of psycho-geriatric elderly
68
Pearson coefficient
0.55
[ 92]
OxCAP-MH
EQ-5D-index UK
EQ-5D-index UK
Austria
Patients in socio-psychiatric services
159
Spearman Rank
0.67
[ 17]
OxCAP-MH
EQ-5D-index DE
EQ-5D-index DE
Austria
Patients in socio-psychiatric services
160
Spearman Rank
0.66
[ 17]
OxCAP-MH
EQ-5D VAS
EQ-5D VAS
Austria
Patients in socio-psychiatric services
161
Spearman Rank
0.58
[ 17]
OxCAP-MH
BSI-18
BSI-18
Austria
Patients in socio-psychiatric services
162
Spearman Rank
− 67
[ 17]
OxCAP-MH
WHOQOL-BREF Physical health
WHOQOL-BREF Physical health
Austria
Patients in socio-psychiatric services
163
Spearman Rank
0.69
[ 17]
OxCAP-MH
WHOQOL-BREF Psychological
WHOQOL-BREF Psychological
Austria
Patients in socio-psychiatric services
164
Spearman Rank
0.75
[ 17]
OxCAP-MH
WHOQOL-BREF Social relationships
WHOQOL-BREF Social relationships
Austria
Patients in socio-psychiatric services
165
Spearman Rank
0.50
[ 17]
OxCAP-MH
WHOQOL-BREF Environment
WHOQOL-BREF Environment
Austria
Patients in socio-psychiatric services
166
Spearman Rank
0.69
[ 17]
OxCAP-MH
Mini-ICF-APP
Mini-ICF-APP
Austria
Patients in socio-psychiatric services
167
Spearman Rank
− 0.47
[ 17]
OxCAP-MH
Global Assessment of Functioning
GAF
Austria
Patients in socio-psychiatric services
168
Spearman Rank
0.35
[ 17]
OxCAP-MH
EQ-5D-3L Utility
EQ-5D-3L
UK
Patients with psychosis
172
Pearson coefficient
0.45
[ 19]
OxCAP-MH
EuroQol Visual Analogue Scale
EQ-5D-VAS
UK
Patients with psychosis
172
Pearson coefficient
0.52
[ 19]
OxCAP-MH
Brief Psychiatric Rating Scale (negative correlation)
BPRS*
UK
Patients with psychosis
172
Pearson coefficient
0.41
[ 19]
OxCAP-MH
Global Assessment of Functioning
GAF
UK
Patients with psychosis
172
Pearson coefficient
0.24
[ 19]
OxCAP-MH
Objective Social Outcomes Index
SIX
UK
Patients with psychosis
172
Pearson coefficient
0.12
[ 19]
Women’s Capabilities Index
WHOQOL-Bref
WHOQOL-Bref
Malawi
Women from Mchinji, Malawi
20
Pearson correlation
0.62
[ 64]

Appendix 5

See Table  10.
Table 10
Abbreviations of health-related instruments
Short form
Full name of instrument
15D
15D
SF-36
36-Item Short Form Health Survey
ADRQL
Alzheimer’s Disease-Related Quality of Life
AQoL-8D
Assessment of Quality-of-Life Multi-Attribute Utility Instrument
Barthel Index
Barthel Index measure of activities of daily living (ADL)
OPQOL-brief
brief Older People’s Quality of Life
BPRS
Brief Psychiatric Rating Scale
BSI-18
brief symptom inventory 18
Cantril’s Ladder
Cantril’s Ladder
CES
Carer Experience Scale
CSI
Carer Strain Index
CASP-12
Control and autonomy subscale of CASP-12
CTM-3
Care Transitions Measure
DASS-D
Depression, Anxiety and Stress Scale (DASS-D of DASS-21)
EQ-5D + C
EQ-5D extended with a cognitive dimension
EQ-5D-VAS
EuroQol Visual Analogue Scale
GDS-15
15-item Geriatric Depression Scale
GHQ-12
12-item General Health Questionnaire
GAF
Global Assessment of Functioning
HUI-3
Health Utilities Index Mark 3
K10
Kessler Psychological Distress Scale
LDQ
Leeds Dependence Questionnaire
Mini-ICF-APP
Mini-ICF-APP Social Functioning Scale
SIX
Objective Social Outcomes Index
OPQoL-Brief
Older People’s Quality-of-Life brief questionnaire (13 items)
OHS
Oxford Hip Score
PDQ-39
Parkinson’s specific Quality of Life
RAS-P
Recovery Assessment Scale
SF-6D
Short Form Six Dimension
SSQ
Social Satisfaction Questionnaire
SWLS
Satisfaction with Life Scale
WOMAC
Western Ontario and McMaster Universities
WHOQOL-Bref
World Health Organization Quality-of-Life Instruments - abbreviated version

Appendix 6

See Table  11.
Table 11
Details of applied evaluations
Author, Year
Country
Disease
Intervention
Population
Perspective
Capability measure
Time points
Missing data
Barnes, 2016
UK
Schizophrenia
Citalopram (ACTIONS trial)
Adult patients
Societal
ICECAP-A
Baseline; 12–36–48 weeks
Multiple imputation
Bray, 2017
UK
Visual impairment
Portable electronic vision enhancement system (compared with optical low vision aids)
Adult patients
Societal
ICECAP-A
Baseline; 2 months; 4 months
Not reported
Burns, 2016
UK
Psychosis
Community treatment orders
Adult patients
Health and social care
OxCAP-MH
Baseline; 6 months; 12 months
Multiple imputation
Goranitis, 2017
UK
Drug addiction
2 Psychological interventions relative to usual care
Treatment resistant adult addicts
Health and social care
ICECAP-A
Baseline; 12 months
Chained equations with predictive mean matching
Henderson, 2013
UK
Heart failure, chronic obstructive pulmonary disease, or diabetes
Community-based telehealth (Whole Systems Demonstrator)
People with a long-term condition
Societal
ICECAP-O
Baseline; 12 months
Multiple imputation
Makai, 2014
Netherlands
Health decline in the elderly
Walcheren integrated care model
Frail elderly
Societal
ICECAP-O
Baseline, 3 months
Not reported
Parker, 2019
UK
Diabetic plantar ulceration
Traditional vs. digital foot orthoses
Adult patients
Healthcare provider
ICECAP-A
Baseline; 6 months
Not reported
Patty, 2018
Netherlands
Visual impairment
ICT training
Adult patients
Societal
ICECAP-O
3 months; post-intervention; pre-study
Not reported
Simon, unpublished
UK
Schizophrenia or schizoaffective disorder and depression
Positive Memory Training (PoMeT)
Adult patients
(1) Healthcare, (2) Health and social care, (3) Broader societal
ICECAP-A and OxCAP-MH
Baseline, 3, 6 and 9 months
Stepwise approach
Williams, 2016
UK
Hip fracture
Multidisciplinary rehabilitation package following hip fracture
Older adults (aged ≥ 65)
Healthcare provider
ICECAP-O
Baseline, 3 months
Not reported

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