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Abstract
Time Trade-Off (TTO) valuations of health are widely used in economic evaluation of
health care. Current approaches to eliciting TTO values, and their use in economic
evaluation, rest on specific assumptions about the way utility relates to time and
health. Both the assumptions themselves and evidence of violations of them are discussed
in the literature - yet the issues appear not to be widely appreciated by those using
and applying TTO in economic evaluation. This paper adds to that literature by demonstrating
both the requirements of TTO and violations of these assumptions in terms of the underlying
indifference curve maps and utility functions. The advantage of this approach is that
it demonstrates very clearly a number of fundamental problems for the way TTO values
are currently elicited and used in cost utility analysis. In essence, it is extremely
unwise to assume that the current 'tariffs' of TTO values, such as those widely used
in cost utility analysis to inform health sector decisions in many countries can be
applied irrespective of the duration of the health states to which they are assigned.
The estimates of QALYs that result will, quite often, simply be wrong. We conclude
by pointing to a number of possible solutions.