Can we estimate the 'social' value of a QALY?

There is growing interest in estimating the 'societal' willingness to pay (WTP) for a quality adjusted life year (QALY) to help public health system decision-makers determine whether a health care programme should/not be undertaken. However, there is a lack of clarity in this debate concerning four core issues: (i) is 'social' WTP simply the sum of 'individual' WTP; (ii) will 'individual' WTP map directly into 'social' WTP; (iii) is 'personal' income the appropriate budget constraint; (iv) should WTP be adjusted for ability to pay? This paper outlines the relevance and importance of each of these issues in the hope of encouraging a wider debate on the core issues that empirical studies will have to explore to discover whether such a value may be obtained.