Productivity costs in health-state valuations : does explicit instruction matter?

There has been considerable debate on whether productivity costs should be captured in the numerator or the denominator of the cost-effectiveness ratio. That debate cannot be resolved on the basis of theoretical arguments alone because the final choice also depends on what is incorporated in health-state valuations by respondents and how this influences outcomes. At the moment, little is known about whether the effects of ill health on income are included in health-state valuations, and how instructions on including or excluding the effects on income influence health-state valuations.

To conduct an empirical study of health-state valuations to test: (i) whether or not respondents spontaneously include the effect of ill health on income and leisure time; (ii) the impact on the valuation of inclusion (or exclusion) of such effects; and (iii) the influence of explicit instructions on this matter.

Three questionnaires were developed and administered to the general public. Health-state valuations were conducted by visual analogue scale scoring of three health states of differing severity taken from the EQ-5D. Version 1 had no directions regarding inclusion/exclusion of effects of ill health on income. Those respondents who spontaneously included effects on income were subsequently asked to value the same three health states again, excluding these effects. Version 2 had explicit instructions to incorporate the effects on income. Version 3 stated that income was assumed to not change as a result of ill health. Respondents for versions 2 and 3 were also questioned about inclusion of effects on leisure time.

Giving explicit instructions on the incorporation or exclusion of effects of ill health on income did not lead to significant differences in subsequent health-state valuations. In the absence of instruction, 36% of respondents included and 64% excluded effects on income, but the health-state valuations of the two groups were not significantly different. Eighty-four percent of respondents included the effects of ill health on leisure activities, and again this had no significant impact on the resulting health-state valuations.

It appears that neither spontaneous differences in incorporation of effects on income, nor explicit instructions will yield significantly different health-state valuations. This may suggest that QALY measures are insensitive to concerns regarding effects on income even when these are (explicitly) incorporated, and these effects may therefore be best placed on the cost side of the cost-effectiveness ratio.