中華心理學刊 民 86，39 卷，2 期，173-192
Chinese Journal of Psychology 1997, Vol.39, No.2, 173-192

Peter H. Schönemann（Department of Psychology, National Taiwan University）

Abstract

Recent work on hit rates and base rates (Schönemann and Thompson. 1996) is extended: A flawed premise in the derivation of an earlier hit rate approximation, HR1, is corrected, leading to a slightly more complicated approximation, HR2. However. over the targeted parameter region, the differences between HR I and HR2 are small. After deriving exact hit rates for 2x2 contingency tables with binary criteria, they are compared with HR I and HR2. and also with hit rates for continuous criteria infer red, via Bayes' Theorem, from Taylor and Russell's (1939) table s. Overall, the simpler approximation HR I outperforms HR2. Finally, a new approximation is derived for the minimum validity needed that a test improves over random admissions in terms of total percent of correct classifications. More than four decades ago, Meehl and Rosen (1955) warned that validity coefficients, in isolation , are in sufficient for gauging the practical merit of a test, be ca use, ' ... when the base rates of the criterion classification deviate greatly from a 50 percent split, use of a test sign having slight or moderate validity will result in an increase of erroneous clinical decisions.' (p. 215. Emphasis in the original). The present results corroborate these concerns.

Keywords：Mental tests, IQ tests, Hit rate bias, Base rate problems, Predictive validities