Substantial risk of "Accidental MCI" in healthy older adults: base rates of low memory scores in neuropsychological assessment.

When assessing older adults for mild cognitive impairment (MCI) or dementia, it is important to understand how often low memory scores are obtained in healthy people in order to minimize false positive diagnoses. This study examines the base rates of low memory scores in older adults across a battery of memory tests. Participants included older adults (55-79 years; N = 742) from the Neuropsychological Assessment Battery (NAB; Stern and White, 2003a) standardization sample. The NAB Memory Module consists of four co-normed memory tests (i.e., List Learning, Shape Learning, Story Learning, and Daily Living Memory) yielding 10 demographically corrected T-scores. When all 10 T-scores were examined simultaneously, 55.5% of older adults had one or more scores one standard deviation (SD) below the mean. At <1.5 SDs, 30.8% of healthy older adults obtained one or more low memory scores. Obtaining low memory scores occurs more often with lesser intellectual abilities. For example, 56.5% of older adults with low average intellectual abilities obtained one or more low memory scores (<1.5 SDs) compared to 21.1% with high average intellectual abilities. Understanding the base rates of low scores can reduce over-interpretation of isolated low memory scores and minimize false positive diagnoses of MCI.