Journal Article

To Err is Human: “Abnormal” Neuropsychological Scores and Variability are Common in Healthy Adults

Laurence M. Binder, Grant L. Iverson and Brian L. Brooks

in Archives of Clinical Neuropsychology

Published on behalf of The National Academy of Neuropsychology

Volume 24, issue 1, pages 31-46
Published in print February 2009 | ISSN: 0887-6177
Published online March 2009 | e-ISSN: 1873-5843 | DOI:
To Err is Human: “Abnormal” Neuropsychological Scores and Variability are Common in Healthy Adults

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Normative studies of variability in performance by healthy adults on neuropsychological batteries are reviewed. Regarding test score scatter, normative participants often have large discrepancies between best and worst scores. When “abnormality” was defined as a score more than one standard deviation below the mean, in test batteries with at least 20 measures, the great majority of normative participants had one or more abnormalities. Restricting samples to participants with above average IQ or educational levels and using more conservative definitions of abnormality, such as two standard deviations below the mean did not eliminate the presence of abnormal scores. We conclude that abnormal performance on some proportion of neuropsychological tests in a battery is psychometrically normal. Abnormalities do not necessarily signify the presence of acquired brain dysfunction because low scores and large intraindividual variability often are characteristic of healthy adults. We recommend that test battery developers provide data on the amount of variability in normal samples and also provide base rate tables with false positive rates that can be used clinically when interpreting test performance.

Keywords: Normal variability; Normal cognitive function; Misdiagnosis; Prevalence of abnormal scores; Base rates

Journal Article.  11807 words. 

Subjects: Neuroscience ; Neuropsychology

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