Performance of non-neurological older adults on the Wisconsin Card Sorting Test and the Stroop Color-Word Test: normal variability or cognitive impairment?

There is currently no standard criterion for determining abnormal test scores in neuropsychology; thus, a number of different criteria are commonly used. We investigated base rates of abnormal scores in healthy older adults using raw and T-scores from indices of the Wisconsin Card Sorting Test and Stroop Color-Word Test. Abnormal scores were examined cumulatively at seven cutoffs including >1.0, >1.5, >2.0, >2.5, and >3.0 standard deviations (SD) from the mean as well as those below the 10th and 5th percentiles. In addition, the number of abnormal scores at each of the seven cutoffs was also examined. Results showed when considering raw scores, ∼15% of individuals obtained scores>1.0 SD from the mean, around 10% were less than the 10th percentile, and 5% fell >1.5 SD or <5th percentile from the mean. Using T-scores, approximately 15%-20% and 5%-10% of scores were >1.0 and >1.5 SD from the mean, respectively. Roughly 15% and 5% fell at the <10th and <5th percentiles, respectively. Both raw and T-scores>2.0 SD from the mean were infrequent. Although the presence of a single abnormal score at 1.0 and 1.5 SD from the mean or at the 10th and 5th percentiles was not unusual, the presence of ≥2 abnormal scores using any criteria was uncommon. Consideration of base rate data regarding the percentage of healthy individuals scoring in the abnormal range should help avoid classifying normal variability as neuropsychological impairment.