The capability approach is an approach to assessing well-being developed by Amartya Sen. Interest in this approach has resulted in several attempts to develop questionnaires to measure and value capability at an individual level in health economics. This commentary critically reviews the ability of these questionnaires to measure and value capability. It is argued 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. It may be practically more feasible to measure and value capability approximately rather than directly. Suggestions are made on how to measure and value an approximation to capability, but further research is required to implement the suggestions.
