Do individuals consider expected income when valuing health states?

The purpose of this study was to empirically explore whether individuals take their expected income into consideration when directly valuing predefined health states. This was intended to help determine how to handle productivity costs due to morbidity in a cost-effectiveness analysis.

Two hundred students each valued four hypothetical health states by using time trade-off (TTO) and a visual analogue scale (VAS). The students were randomly assigned to two groups. One group was simply asked, without mentioning income, to value the different health states (the non-income group). The other group was explicitly asked to consider their expected income in relation to the health states in their valuations (the income group).

For health states that are usually assumed to have a large effect on income, the valuations made by the income group seemed to be lower than the valuations made by the non-income group. Among the students in the non-income group, 96 percent stated that they had not thought about their expected income when they valued the health states. In the income group, 40 percent believed that their expected income had affected their valuations of the health states.

The results show that, as long as income is not mentioned, most individuals do not seem to consider their expected income when they value health states. This indicates that productivity costs due to morbidity are not captured within individuals' health state valuations. These findings, therefore, suggest that productivity costs due to morbidity should be included as a cost in cost-effectiveness analyses.