Improving the sensitivity of the time trade-off method: results of an experiment using chained TTO questions.

We test a chained time trade-off (TTO) approach to estimating health gains from interventions by asking respondents to directly compare the "before" and "after" intervention health states in the TTO framework. Respondents with experience of both health states were used, thus minimising biases stemming from confusion surrounding health descriptions. We found that responses to these direct comparisons were much more likely to capture a perceived change in health status than the conventional approach to TTO estimation. This is an important finding because the TTO method is preferred by practitioners to many other direct generic methods of health status valuation both on empirical grounds and because it is based on the notion of opportunity cost, which is central to consumer theory, requiring respondents to express their preferences in terms of foregoing some of one good in exchange for more of another (unlike a rating scale).