Assessing Convergent Validity of Health-state Utilities Obtained Using Different Scaling Methods

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Abstract
A number of empirical studies have attempted to assess the convergent validity of health-state utilities obtained using two or more scaling methods (standard gamble, time tradeoff, rating scale, magnitude estimation, equivalence technique, and willing ness-to-pay). The data from these studies can be mapped onto an N x K matrix, where N and K are the numbers of respondents and health states, respectively, and each matrix cell consists of a pair of health-state utilities, one obtained using scaling method X and the other obtained using scaling method Y. The Pearson's r assessing convergent validity can then be computed as 1) the unraveled correlation over all N x K data pairs, 2) the mean within-respondent correlation, 3) the mean within-health- state correlation, or 4) the correlation of the across-respondents means. These four different ways of computing the correlation do not necessarily yield the same results. The appropriateness of each method of computing the correlation is considered. Key words: convergent validity; equivalence technique; health-state preferences; health- state utilities; magnitude estimation; person tradeoff; rating scale; scaling; standard gamble; time tradeoff; willingness-to-pay. (Med Decis Making 1999;19:487-496)