Cross-validation of prediction equations for Wechsler Memory Scale-III Indexes

Six prediction equations were previously found to predict to Wechsler Memory Scale-III (WMS-3) Immediate Memory Index (IM) and General Memory Index (GM) using two- or three-subtest combinations. The equations were cross-validated on a sample of 214 mixed clinical patients from an entirely different location in the Midwest. The two three-subtest prediction equations (including Logical Memory, Verbal Paired Associates, and either Faces or Family Pictures) better estimated IM and GM than did the two-subtest equations (Logical Memory and Verbal Paired Associates). Correlations for the former equations correlated .97 and .96 with full WMS-3 IM and GM, respectively. In addition, at least 95% of the predicted scores were within two SEMs of obtained IM and GM scores. The two-subtest equations correlated only .89 for IM and .92 for GM. The predicted scores that fell within two SEMs captured 78% and 88% of the cases for IM and GM, respectively. The results provide support for the use of the three-subtest prorated forms of the WMS-3 to estimate IM and GM.