Individual differences in the use of the response scale determine valuations of hypothetical health states: an empirical study

ABSTRACT: BACKGROUND: The literature remains inconclusive about the effects of socio-demographic characteristics of the respondent, including age, on valuation scores of hypothetical health states. We analyzed data from a study designed to discriminate between the effects of respondents age and time preference on valuations of health states to get insight in the contribution of individual response patterns to the variance in valuation scores. METHODS: 212 respondents from different age groups valued six hypothetical health states with three methods: a Visual Analogue Scale (VAS) and two variants of the Time trade-off (TTO). Analyses included a generalizability study, principal components analysis and cluster analysis. RESULTS: Valuation scores differed significantly but not systematically between valuation methods. A total of 36.8% of variance was explained by health states, 1.6% by elicitation method and 0.2% by age group. Individual differences in the use of the response scales, e.g. a tendency to give either high or low TTO-scores, or a high or low scoring tendency on the VAS were the main source of remaining variance. These response patterns were not related to age or other identifiable respondent characteristics. CONCLUSIONS: We conclude that individual response patterns were more important determinants of TTO or VAS valuations of health states than age or other measured respondent characteristics. Further valuation research should focus on explaining individual response patterns as a possible key to understanding the determinants of health state valuations.