Test-retest reliability of health state valuation techniques: the time trade off and person trade off.

Economic analysis is increasingly being employed in formal resource allocation decision-making processes in health care. As a consequence, the methods employed by economic analysts are increasingly subject to close scrutiny. One such area of methodology concerns the instruments used to elicit preferences for various health states for use in the construction of quality-adjusted life years. There are a number of techniques which may be used to elicit preferences and different techniques produce different results. The objective of this study was to explore the test-retest reliability of two techniques: Time Trade Off (TTO) and Person Trade Off (PTO) valuations were collected by a general population postal survey. A total of 798 respondents returned questionnaires. The intra class correlation coefficients ranged from 0.40 to 0.88 for TTO and, -0.17 to 0.82 for PTO, with the majority of coefficients being >0.50. The reliability coefficients varied between techniques and health states, with the TTO technique tending to produce higher coefficients. While the reliability results for TTO were generally positive, the reliability results for PTO are less clear.