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Examining the range of normal intraindividual variability in neuropsychological test performance

Published online by Cambridge University Press:  27 August 2003

David J. Schretlen ,
Cynthia A. Munro ,
James C. Anthony  and
Godfrey D. Pearlson
David J. Schretlen*
Affiliation:
Department of Psychiatry and Behavioral Sciences, Johns Hopkins University School of Medicine, Baltimore, Maryland
Cynthia A. Munro
Affiliation:
Department of Psychiatry and Behavioral Sciences, Johns Hopkins University School of Medicine, Baltimore, Maryland
James C. Anthony
Affiliation:
Department of Psychiatry and Behavioral Sciences, Johns Hopkins University School of Medicine, Baltimore, Maryland Department of Mental Hygiene, Johns Hopkins University School of Public Health, Baltimore, Maryland
Godfrey D. Pearlson
Affiliation:
Department of Psychiatry and Behavioral Sciences, Johns Hopkins University School of Medicine, Baltimore, Maryland Department of Mental Hygiene, Johns Hopkins University School of Public Health, Baltimore, Maryland
*
*Reprint requests to: David J. Schretlen, Ph.D., Johns Hopkins Hospital, 600 N. Wolfe St., Meyer 218, Baltimore, MD 21287-7218. E-mail: dschret@jhmi.edu
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Abstract

Neuropsychologists often diagnose cerebral dysfunction based, in part, on marked variation in an individual's cognitive test performance. However, little is known about what constitutes the normal range of intraindividual variation. In this study, after excluding 54 individuals with significant health problems, we derived 32 z-transformed scores from 15 tests administered to 197 adult participants in a study of normal aging. The difference between each person's highest and lowest scores was computed to assess his or her maximum discrepancy (MD). The resulting MD values ranged from 1.6 to 6.1 meaning that the smallest MD shown by any person was 1.6 standard deviations (SDs) and the largest MD shown by any person was 6.1 SDs. Sixty-six percent of participants produced MD values that exceeded 3 SDs. Eliminating each person's highest and lowest test scores decreased their MDs, but 27% of the participants still produced MD values exceeding 3. Although MD values appeared to increase with age, adjusting test scores for age, which is standard in clinical practice, did not correct for this. These data reveal that marked intraindividual variability is very common in normal adults, and underscore the need to base diagnostic inferences on clinically recognizable patterns rather than psychometric variability alone. (JINS, 2003, 9, 864–870.)

Keywords

NeuropsychologyClinical inferenceIntraindividual variability
Type
Research Article
Information
Journal of the International Neuropsychological Society , Volume 9 , Issue 6 , September 2003 , pp. 864 - 870
Copyright
Copyright © The International Neuropsychological Society 2003

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