Wellbeing or Capability Instrument

Wellbeing or Capability Instrument in Economic Evaluation Beyond Health

Health economists turn to wellbeing and capability instruments when the main benefit of a programme lies outside health, as with social care, public health, carer support, housing or community services. In a Coventry household survey analysed by Johnson and colleagues, about 75 per cent of 7,469 participants scored the maximum on the EQ-5D-3L while their mental wellbeing varied greatly, so for most of them the EQ-5D-3L had no room left to register an improvement. The class covers several different constructs, chiefly capability wellbeing (ICECAP), mental and subjective wellbeing (WEMWBS, SWEMWBS and life satisfaction), social care-related quality of life (ASCOT) and the broader health and wellbeing items of the EQ-HWB. Each scale has its own anchors and feeds its own outcome currency, so the choice of instrument decides whether a result can sit inside a cost-utility analysis, beside it, or in a cost-benefit appraisal of a different kind.

Capability, wellbeing and health-related quality of life

A measure of health-related quality of life such as the EQ-5D describes health problems, and its value sets score states on a scale where 1 is full health and 0 is dead. Brazier and colleagues opened their 2022 account of the EQ-HWB by observing that existing measures for estimating QALYs are mostly limited to health-related quality of life. Instruments in this class widen what is described, and they do it in different ways.

Capability instruments such as ICECAP-O for older people and ICECAP-A for adults ask what a person is able to do and be, so a capability score records the options open to a person whether or not they are used.

Wellbeing instruments ask how life is going or how a person feels. Subjective wellbeing can be measured with single questions such as the four personal wellbeing questions of the Office for National Statistics, each answered on a 0 to 10 scale, of which life satisfaction is the evaluative measure. Mental wellbeing scales such as WEMWBS and SWEMWBS sum items about positive aspects of mental health, the EQ-HWB adds wellbeing items to health items, and ASCOT describes social care-related quality of life at the edge of the class.

Welfarism, extra-welfarism and the space being evaluated

The choice of instrument is a choice about the evaluative space, the set of outcomes an analysis treats as valuable. Coast, Smith and Lorgelly traced how the capability approach has spread through health economics. They describe Culyer as drawing on the capability approach to develop the extra-welfarist perspective, which gives the theoretical basis for using QALYs and which NICE accepts for its evaluations. They also argue that the application stayed indirect, because the focus remained narrowly on health functioning and the rule remained maximisation.

Capability instruments widen that space beyond health, while subjective wellbeing measures rest on how people themselves evaluate their lives. The two can rank one programme differently, since a person who could see friends but chooses not to scores well on capability and may score poorly on life satisfaction.

Outcome currencies built from these instruments

Each instrument becomes an outcome currency once its score is multiplied by time, in the same way that utilities become QALYs. The gain between two options takes one general form.

$$\Delta O = \sum_{j=1}^{J} \left( s^{A}_{j}-s^{B}_{j} \right) t_{j}$$

where $\Delta O$ is the gain in the instrument's own unit, $J$ is the number of periods, $s^{A}_{j}$ and $s^{B}_{j}$ are the mean scores with options A and B in period $j$, and $t_{j}$ is the length of period $j$ in years.

The unit depends on the score that goes in. The ICECAP developers call the product of their capability index values and time Years of Full Capability (YFC), which they state is not equivalent to a QALY. Mitchell, Roberts, Barton and Coast developed Years of Sufficient Capability (YSC), which credit capability only up to a sufficient level. Yiu and colleagues present the Mental Well-being Adjusted Life Year (MWALY), built on a UK value set for SWEMWBS, as an alternative outcome measure to the QALY. HM Treasury's supplementary Green Book guidance on wellbeing defines a wellbeing year (WELLBY) as a one-point change in life satisfaction on a 0 to 10 scale, per person per year, discounted at the Green Book health discount rate. ASCOT and the EQ-HWB-S keep the anchor at dead, yet each counts different effects from the EQ-5D, so their units are not interchangeable with EQ-5D QALYs.

Illustrative worked example of one programme in three currencies

All numbers in this example are illustrative and undiscounted. A community support programme for working-age adults living alone costs GBP 900 more per person than usual care, and its effects last 2 years. The trial collects the EQ-5D, ICECAP-A and the ONS life satisfaction question.

1. QALYs. The mean utility gain is 0.01 a year, so the gain is 0.01 × 2 = 0.02 QALYs and the ratio is 900 ÷ 0.02 = 45,000, or GBP 45,000 per QALY.

2. Years of Full Capability. The mean ICECAP-A gain is 0.05 a year, so the gain is 0.05 × 2 = 0.10 YFC and the ratio is 900 ÷ 0.10 = 9,000, or GBP 9,000 per YFC.

3. WELLBYs. Mean life satisfaction rises by 0.4 points a year, so the gain is 0.4 × 2 = 0.8 WELLBYs and the ratio is 900 ÷ 0.8 = 1,125, or GBP 1,125 per WELLBY.

The three ratios describe one programme but cannot be ranked against each other, because each denominator is in a different unit. Only the first can be compared with the cost per QALY thresholds NICE uses, and on that basis the programme looks poor value. NICE has not adopted a threshold for a cost per YFC, so the second result can only be compared with other programmes measured on ICECAP-A. The WELLBY result belongs to a different decision framework, since the Green Book guidance supplies a monetary value per WELLBY for cost-benefit analysis, in which benefits are converted to money and set against costs. A committee shown all three in a cost-consequence analysis can see that most of the benefit lies outside health.

When decision makers accept wellbeing and capability evidence

NICE's guideline manual, Developing NICE guidelines (PMG20), states that for some decision problems, such as interventions with a social care focus, the intended outcomes are broader than improvements in health status. Its reference case table, table 7.1 in section 7.4, has three columns. In the row on measuring non-health effects, the first column reads not applicable, the column for public-sector interventions with health and non-health outcomes says such effects are to be decided on a case-by-case basis where appropriate, and the column for interventions with a social care focus names capability or social care-related quality of life measures, such as ICECAP or ASCOT, when an intervention results in both health and capability or social care outcomes. PMG20 now says that an interim methods statement on the EQ-5D-5L takes precedence over it and that section 7.4 (table 7.1) will be updated, so the table is under revision.

NICE's science policy pages describe the EQ-HWB as a new standardised measure of health and wellbeing created following the Extending the QALY project, state that it has not been developed as a replacement for the EQ-5D but as a different instrument that captures a broader range of impacts on people, their families and carers, and say research to validate it will help NICE decide whether and how to use it in future evaluations. NICE has not adopted the EQ-HWB in its reference case.

Use has lagged behind permission. Zhang and colleagues reviewed NICE social care and public health guidelines published before 26 August 2025 and found ICECAP as an outcome in 1 per cent of eligible guidelines and ASCOT in 4 per cent, with neither significantly affecting committee decisions.

Outside health technology assessment, HM Treasury's wellbeing guidance, first published in July 2021 and revised in November 2022, sets out how wellbeing impacts can be assessed and, where the evidence allows, monetised for cost-benefit analysis, within the Green Book five case model. The background paper published with it recommends a range of values per WELLBY, with the lower bound set to be as consistent as possible with the Green Book's recommended QALY value.

Choosing an instrument for a trial or model

The decision problem and the perspective set the choice. A QALY-based reference case needs a health utility measure as the primary outcome, so a wellbeing or capability instrument adds a secondary result, while a social care or cross-government appraisal may put the broader measure first.

Helter and colleagues found no consensus on the most appropriate way to use capability instruments in economic evaluation. Collecting a health utility measure and a broader measure in the same study keeps the reference-case result available while showing what it leaves out.

How the class differs from neighbouring ideas

A generic instrument such as the EQ-5D is a health status questionnaire applicable across diseases, generic about conditions but still limited to health. A wellbeing or capability instrument is defined by reaching beyond health, whether or not it is generic across conditions. Preference-based scoring alone does not put a score on the QALY scale, which is anchored at dead. ASCOT and the EQ-HWB-S use that anchor, while ICECAP index values are preference-based but anchored at no capability, and WEMWBS totals and life satisfaction ratings carry no preference weights. Measures of caregiver quality of life are designed for carers alone, whereas the EQ-HWB was developed to be completed in the same form by patients, social care users and carers.

Limitations and common misreadings

The commonest errors come from treating every score in the class as a health utility. Each error changes the result an analysis reports.

• Calling every currency a QALY. YFCs, YSCs, MWALYs and WELLBYs each have their own units and anchors. The ICECAP developers state that a YFC is not equivalent to a QALY, and Yiu and colleagues present the MWALY as an alternative to it.
• Borrowing the QALY threshold. A cost per YFC or per WELLBY compared with a cost per QALY threshold mixes units, as the worked example shows.
• Adding broad and health outcomes together. A wellbeing gain and a QALY gain measured in the same people overlap, so summing them double counts the health effects that both instruments register.
• Ignoring the sufficiency choice. Maximising capability and securing sufficient capability can rank the same programmes differently, and the rule used should be stated.
• Mixing versions and value sets. Several instruments exist in more than one version with differing value sets, and the EQ-HWB-S value set is still a pilot.

Sources

• Brazier J, Peasgood T, Mukuria C, et al. The EQ-HWB: overview of the development of a measure of health and wellbeing and key results. Value in Health. 2022;25(4):482-491. doi:10.1016/j.jval.2022.01.009
• Coast J, Smith RD, Lorgelly P. Welfarism, extra-welfarism and capability: the spread of ideas in health economics. Social Science and Medicine. 2008;67(7):1190-1198. doi:10.1016/j.socscimed.2008.06.027
• Helter TM, Coast J, Łaszewska A, et al. Capability instruments in economic evaluations of health-related interventions: a comparative review of the literature. Quality of Life Research. 2020;29(6):1433-1464. doi:10.1007/s11136-019-02393-5
• HM Treasury. Green Book supplementary guidance: wellbeing, including Wellbeing guidance for appraisal. Published 26 July 2021, last updated 18 November 2022. https://www.gov.uk/government/publications/green-book-supplementary-guidance-wellbeing
• HM Treasury. Wellbeing guidance for appraisal: background paper reviewing methods and approaches. July 2021. https://assets.publishing.service.gov.uk/media/60fa91c68fa8f50431ca80da/Wellbeing_guidance_for_appraisal_-_background_paper_reviewing_methods_and_approaches.pdf
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• National Institute for Health and Care Excellence. Developing NICE guidelines: the manual (PMG20), chapter 7 Incorporating economic evaluation, section 7.4 and table 7.1. Last updated 23 October 2025. https://www.nice.org.uk/process/pmg20/chapter/incorporating-economic-evaluation
• National Institute for Health and Care Excellence. Science policy and methods projects (web page, EQ-HWB entry). https://www.nice.org.uk/what-nice-does/our-research-work/our-projects-and-partners/science-policy-projects (accessed 17 October 2026)
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