The Association Between the Number of Neuropsychological Measures and the Base Rate of Low Scores.

Obtaining one or more low scores, or scores indicative of impairment, is common in neuropsychological batteries that include several measures even among cognitively normal individuals. However, the expected number of low scores in batteries with differing number of tests is unknown. Using 10 neuropsychological measures from the National Alzheimer's Coordinating Center database, 1,023 permutations were calculated from a sample of 5,046 cognitively normal individuals. The number of low scores (i.e., z score ≤-1.5) varied for the same number of measures and among different number of measures and did not increase linearly as the number of measures increased. According to the number of low scores shown by fewer than 10% of the sample, cognitive impairment should be suspected for 1 or more, 2 or more, and 3 or more in batteries with up to 2 measures, 3 to 9 measures, and 10 measures, respectively. These results may increase the identification of mild cognitive impairment.