Implications of within-person variability in cognitive and neuropsychological functioning for the interpretation of change.

Abstract

Samples of adults across a wide age range performed a battery of 16 cognitive tests in 3 sessions within an interval of approximately 2 weeks. Estimates of within-person variability across the 3 assessments were relatively large and were equivalent in magnitude to the cross-sectional age differences expected over an interval of 15-25 years. These findings raise questions about the precision of assessments based on a single measurement and imply that it may be difficult to distinguish true change from short-term fluctuation. Because there were large individual differences in the magnitude of this variability, it is proposed that change might be most meaningfully expressed in units of each individual's own across-session variability. Keywords cognition; aging; longitudinal change; measurement burstSeveral recent articles have reported the existence of substantial within-person variability in performance on the same cognitive and neuropsychological tests across multiple occasions. To illustrate, in studies by Salthouse and colleagues, the within-person (across-session) standard deviation averaged about 50% of the between-person standard deviation for a variety of different cognitive variables (e.g., Nesselroade & Salthouse, 2004;Salthouse & Berish, 2005;Salthouse, Nesselroade, & Berish, 2006). This phenomenon of sizable within-person variability is interesting for at least three reasons. First, measures of within-person variability could have unique diagnostic significance compared with measures of central tendency. That is, how much a person's performance varies around his or her average level on a specific test could be an early predictor of impending change to a different level of functioning. Consistent with this interpretation are several reports of significant relations between measures of within-person variability and neurological status (e.g., Burton, Strauss, Hultsch, Moll, & Hunter, 2006;Hultsch, MacDonald, Hunter, Levy-Bencheton, & Strauss, 2000;Murtha, Cismaru, Waechter, & Chertkow, 2002;Strauss, MacDonald, Hunter, Moll, & Hultsch, 2002) and even risk of death (Shipley, Der, Taylor, & Deary, 2006).A second reason why within-person variability is important is that it suggests that single assessments may not be sufficient for accurate evaluation of an individual if another assessment with the same test could lead to a different level of performance and, possibly, to a different diagnostic classification. Little is currently known about the potential impact of this type of problem, but it will likely depend on both the magnitude of the variability and the range of variables that exhibit within-person variability.Correspondence concerning this article should be addressed to Timothy A. Salthouse, Department of Psychology, 102 Gilmer Hall, University of Virginia, Charlottesville, VA 22904-4400.. NIH Public Access Author ManuscriptNeuropsychology. Author manuscript; available in PMC 2013 November 25. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author ManuscriptA third reason why the phenom...

Adult age trends in the relations among cognitive abilities.

“…The dataset was aggregated from seven different studies conducted since 2001 at the Cognitive Aging Lab at the University of Virginia (Salthouse, 2007;Salthouse, Atkinson, & Berish, 2003;Salthouse, Berish, & Siedlecki, 2004;Salthouse & Ferrer-Caja, 2003;Salthouse, Nesselroade, & Berish, 2006;Salthouse, Pink, & Tucker-Drob, in press;Salthouse & Siedlecki, 2007;Salthouse, Siedlecki, & Krueger, 2006). Participants were recruited with newspaper advertisements, flyers, and referrals from other participants.…”

Working memory and intraindividual variability in processing speed: A lifespan developmental and individual-differences study

“…There is still some controversy with respect to age differences in older adults. Note, however, that those studies that have reported a lack of age differences in IIV either have relied on accuracy scores rather than RTs in experimental tasks (e.g., Robertson, Myerson, & Hale, 2006) or have studied variability in a task repeated within a short period of time; in the latter case, IIV was computed on relatively few occasions and/or on the number of correct responses within a limited time rather than on RTs (e.g., Salthouse, 2007;Salthouse & Berish, 2005;Salthouse & Nesselroade, 2010).…”

Contributions of the Individual Differences Approach to Cognitive Aging

“…Some of these effects can be illustrated with a comparison of reliabilities of measures across different types of aggregation. Because participants in VCAP performed different versions of the same tests on three sessions each separated by approximately 1 week (e.g., Salthouse, 2007), reliability can be assessed with the correlation of relevant scores across the first and second sessions. The across-session correlations were .75 for a measure of word recall based on the sum of items recalled across 4 repetitions of the same 12-word list; .85 for a composite memory measure based on the average z-score for word recall, paired associates, and logical memory measures; and .96 for a latent variable based on the same 3 memory measures.…”