Purpose: Uncertainty over whether productivity effects are entirely subsumed in quality of life (QOL) measures has led to different standards for measurement in Europe and the US. We use empirical data to explain differences in QOL results when productivity and income are excluded versus explicitly included in QOL assessments.

Methods: The Time Trade-Off method (TTO) and rating scales were used to assess QOL through a series of scenarios (1) without mention of productivity or income effects, (2) explicitly stating expected productivity effects associated with the QOL scenario, and (3) explicitly stating both the productivity and income effects likely to be associated with the health state described. Respondents answered all three scenarios for each of two disease states: Type II diabetes and migraine headache. Baseline scenarios specifying symptom severity and associated productivity and income estimates were drawn from the published literature. To control for any systematic bias resulting from the order of the scenarios, respondents were randomly assigned to one of three survey versions, each with a different ordering of the scenarios. Analyses included paired t-tests for differences between means and descriptive statistics.

Sample: A convenience sample of 88 faculty, staff and students at the University of North Carolina at Chapel Hill and the University of Rochester completed the surveys.

Results: TTO results were significantly lower when productivity effects were explicitly stated in the Type II diabetes scenario (0.80 versus 0.84, p < 0.05). Once productivity effects were included in the scenario, adding information about likely effects of symptoms on earned income did not change the TTO results significantly. In the case of migraine, however, the TTO did not change when expected productivity and income effects were explicitly stated. 26% of respondents reported identical TTO values, regardless of the explicit statement of productivity goals.

Conclusions: Productivity effects of diabetes do not appear to be subsumed within QOL assessments using the TTO, suggesting that the European approach may be more accurate than the methods recommended by the US Panel on Cost Effectiveness in Health and Medicine. Yet, productivity effects of migraine may be subsumed in the QOL measure. Several explanations are possible for the discrepancy by disease, yet further empirical research is required to definitively address the continuing methods controversy.