The new uniform T scores for the MMPI—2: Rationale, derivation, and appraisal.

Abstract

Although normative distributions of MMPI-2 clinical and content scales tend to be positively skewed, individual scales differ in degree of skewness. The linear T scores in use with the original MMPI preserve these skewness differences, so identical T scores on different scales can have different percentile values (are not «percentile comparable»). This particularly compromises profile interpretations. For the MMPI-2, a Uniform T score (UT score) transformation has been adopted. Its target distribution is the positively skewed composite (or prototypical) linear T score distribution of MMPI-2 clinical scales. UT scores are percentile comparable, yet unlike normalized T scores, depart minimally from the familiar linear T scores. We describe the UT score derivation, report degree of percentile comparability achieved, and argue that the positive skewness of the UT-score distributions, besides minmizing discontinuity, is conceptually meaningful