Digit Symbol-Incidental Learning in the WAIS-III: construct validity and clinical significance

We analyzed WAIS-III/WMS-III standardization data for evidence of the construct validity and clinical utility of the Digit Symbol-Incidental Learning procedures (Pairing and Free Recall). Scores on both tests correlated moderately with WMS-III memory index scores (mean r=.38 for Pairing and .36 for Free Recall). Cutoff scores can be used to identify younger and older adults likely to suffer from memory impairment. In the standardization sample (which excludes neurological patients), these have moderate positive predictive power (averaging .56 if either test yields a positive finding), moderate negative predictive power (.76), and high specificity (.88), but low sensitivity (.35). In a clinical sample, the same cutoff scores were much more sensitive, correctly identifying 88% of a group of patients with Alzheimer's Disease. Examinees who obtain these low scores should receive follow-up memory testing. Very high scores are associated with a reduced risk of memory impairment.