Paul Mark Mitchell

The Development of Capability Measures in Health Economics: Opportunities, Challenges and Progress

Recent years have seen increased engagement amongst health economists with the capability approach developed by Amartya Sen and others. This paper focuses on the capability approach in relation to the evaluative space used for analysis within health economics. It considers the opportunities that the capability approach offers in extending this space, but also the methodological challenges associated with moving from the theoretical concepts to practical empirical applications. The paper then examines three ‘families’ of measures, Oxford Capability instruments (OxCap), Adult Social Care Outcome Toolkit (ASCOT) and ICEpop CAPability (ICECAP), in terms of the methodological choices made in each case. The paper concludes by discussing some of the broader issues involved in making use of the capability approach in health economics. It also suggests that continued exploration of the impact of different methodological choices will be important in moving forward.

Predicting the ICECAP-O capability index from the WOMAC osteoarthritis index: Is mapping onto capability from condition-specific health status questionnaires feasible?

Background. There is a growing interest in the application of the capability approach in health economic analysis. The aim of the research reported here is to assess the feasibility of mapping from a condition-specific questionnaire (Western Ontario and McMaster Universities [WOMAC] Osteoarthritis Index) to a capability well-being questionnaire (ICEpop CAPability measure for Older people [ICECAP-O]). Methods. One hundred five osteoarthritis patients requiring joint replacement completed the 5 attributes on the ICECAP-O (attachment, security, role, enjoyment, and control) and the 3 WOMAC categories (pain, stiffness, and physical function). The prediction data set consisted of baseline scores, whereas follow-up data were used to validate the predictions. The mapping algorithms used ordinary least squares and multinomial logistic regression models to predict the relationship between WOMAC scores, categories, or items and ICECAP-O scores or the 5 ICECAP-O attributes. Results. ICECAP-O scores predicted from WOMAC category scores produced the lowest mapping error statistics (mean absolute error = 0.0832; mean squared error = 0.0142) as well as highest goodness of fit (R2 = 0.3976). Prediction of ICECAP-O attributes from WOMAC category scores was possible for the majority of capability dimensions. The “control” attribute and physical function WOMAC category exhibited the strongest relationship (R2 = 0.2143). The “attachment” attribute proved difficult to predict from any WOMAC category, which is in line with intuition given this attribute captures psychological well-being rather than pain, stiffness, or physical function. Conclusion. This is the first study to investigate the predictive ability of a condition-specific measure of health onto capability. The results presented here suggest it is feasible to map from condition-specific measures to an overall capability index, although WOMAC cannot predict individual capability in its entirety. Although the results here are encouraging for those interested in using ICECAP-O, given the small validation sample size applied, further research will be required to verify these findings.

Applications of the Capability Approach in the Health Field: A Literature Review

The primary aims of this review are to document capability applications in the health field and to explore the objectives and decision-rules of studies measuring capability more broadly. Relevant studies are identified using a literature search strategy known as “comprehensive pearl growing”. All studies with a primary focus on health are assessed individually, whilst a summary narrative analysis of the full review examines the objectives of capability studies. Four distinct groups in the health field are identified in the review: (1) physical activity and diet; (2) patient empowerment; (3) multidimensional poverty and (4) assessments of health and social care interventions. Different approaches to applying mixed methods, selecting capability dimensions and weighting capabilities are found across studies. There is a noticeable non-reliance on health status as a sole indicator of capability in health. In terms of objectives of studies measuring capability, although there is a lack of consistency, an objective related to sufficiency of capabilities appeared most often in the studies found in this review. Even though one of the appeals of the capability perspective is its underspecified nature, this review highlights the challenge of finding a coherent alternative to more established approaches of evaluation.

Assessing the validity of the ICECAP-A capability measure for adults with depression

BackgroundEffectiveness and cost-effectiveness are increasingly important considerations in determining which mental health services are funded. Questions have been raised concerning the validity of generic health status instruments used in economic evaluation for assessing mental health problems such as depression; measuring capability wellbeing offers a possible alternative. The aim of this study is to assess the validity of the ICECAP-A capability instrument for individuals with depression.MethodsHypotheses were developed using concept mapping. Validity tests and multivariable regression analysis were applied to data from a cross-sectional dataset to assess the performance of ICECAP-A in individuals who reported having a primary condition of depression. The ICECAP-A was collected alongside instruments used to measure: 1. depression using the depression scale of the Depression, Anxiety and Stress Scale (DASS-D of DASS-21); 2. mental health using the Kessler Psychological Distress Scale (K10); 3. generic health status using a common measure collected for use in economic evaluations, the five level version of EQ-5D (EQ-5D-5L).ResultsHypothesised associations between the ICECAP-A (items and index scores) and depression constructs were fully supported in statistical tests. In the multivariable analysis, instruments designed specifically to measure depression and mental health explained a greater proportion of the variation in ICECAP-A than the EQ-5D-5L.ConclusionThe ICECAP-A instrument appears to be suitable for assessing outcome in adults with depression for resource allocation purposes. Further research is required on its responsiveness and use in economic evaluation. Using a capability perspective when assessing cost-effectiveness could potentially re-orientate resource provision across physical and mental health care services.

Choice of statistical model for cost-effectiveness analysis and covariate adjustment: empirical application of prominent models and assessment of their results

ContextStatistical models employed in analysing patient-level cost and effectiveness data need to be flexible enough to adjust for any imbalanced covariates, account for correlations between key parameters, and accommodate potential skewed distributions of costs and/or effects. We compare prominent statistical models for cost-effectiveness analysis alongside randomised controlled trials (RCTs) and covariate adjustment to assess their performance and accuracy using data from a large RCT.MethodSeemingly unrelated regressions, linear regression of net monetary benefits, and Bayesian generalized linear models with various distributional assumptions were used to analyse data from the TASMINH2 trial. Each model adjusted for covariates prognostic of costs and outcomes.ResultsCost-effectiveness results were notably sensitive to model choice. Models assuming normally distributed costs and effects provided a poor fit to the data, and potentially misleading inference. Allowing for a beta distribution captured the true incremental difference in effects and changed the decision as to which treatment is preferable.ConclusionsOur findings suggest that Bayesian generalized linear models which allow for non-normality in estimation offer an attractive tool for researchers undertaking cost-effectiveness analyses. The flexibility provided by such methods allows the researcher to analyse patient-level data which are not necessarily normally distributed, while at the same time it enables assessing the effect of various baseline covariates on cost-effectiveness results.

Ethics and Values in Welfarism and Extra-Welfarism

This chapter focuses on the ethical values that underpin different types of economic evaluation. Welfarism, the standard health maximization approach to extra-welfarism, and a capability approach to extra-welfarism are all discussed in terms of the different values incorporated. Alternative decision rules around maximization and sufficiency are also examined. These theoretical discussions are then supplemented by two case studies related to mental health. The first considers the relative priority that might be given to depression treatment relative to a variety of physical health conditions, using both forms of extra-welfarism. The second explores the use of health and capability measures in interventions for drug addiction. The evidence presented indicates that interventions for mental health conditions will receive different priorities where different value judgements form the basis for the economic evaluation. This underlines the importance of these ethical decisions.

The Capability Approach: From Theory to Practice

The conceptual and theoretical appeal of Amartya Sens Capability Approach (CA) is unlikely to be questioned by readers of this journal. What has been questioned about the CA, both by philosophers ...