Abstract

In recent years the concept of intraindividual variability, defined as fluctuations around the average level of performance that are not due to measurement error, has gained much interest in cognitive aging research. In sum, intraindividual variability is a precious source of information, complementary to the mean level of performance, to further our understanding of both normal and pathological cognitive aging. The overall purpose of this article is to familiarize the reader with the notion of intraindividual variability and to provide methodological and analytical knowledge to allow for its scientific investigation. In this article, first, the different kinds of variabilities (interindividual, long-term intraindividual and short-term intraindividual) are discussed. Second, several research examples are reviewed to underscore the importance of studying variability in cognitive aging research. Third, longitudinal evidence is reported to discuss the stability and predictive power of intraindividual variability. Last, the methodological and statistical approaches adopted in this line of research are reviewed.