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Archives of Clinical Neuropsychology Advance Access published online on March 6, 2009
Archives of Clinical Neuropsychology, doi:10.1093/arclin/acn001
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© The Author 2009. Published by Oxford University Press on behalf of the National Academy of Neuropsychology. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org.

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

Laurence M. Bindera,*, Grant L. Iversonb,c and Brian L. Brooksb

a Department of Neurology, Oregon Health & Science University, Beaverton, Oregon, USA
b British Columbia Mental Health & Addiction Services, Vancouver, BC, Canada
c University of British Columbia, Vancouver, BC, Canada

* Corresponding author at: 4900 SW Griffith Drive, Suite 244, Beaverton, OR 97005, USA. Tel: +1-503-626-5246. E-mail address: pdxlarry{at}aol.com (L.M. Binder).


  Abstract

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

Accepted: November 19, 2008


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B. L. Brooks, G. L. Iverson, and T. White
Advanced Interpretation of the Neuropsychological Assessment Battery with Older Adults: Base Rate Analyses, Discrepancy Scores, and Interpreting Change
Arch Clin Neuropsychol, November 1, 2009; 24(7): 647 - 657.
[Abstract] [Full Text] [PDF]


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