Cognitive Development and Individual Variability

The standard approach to cognitive development most frequently consists of cross-sectional studies comparing different ages and groups while restricted to a single task. The necessity to focus on the individual in an idiographic perspective, rather than on the task or the variable, has been repeatedly emphasized, most recently in several very important papers by Nesselroade and Molenaar. Variability has also emerged as a crucial characteristic. Moreover, understanding the developmental construction of a given cognitive achievement is imperative to understanding cognitive functioning in adulthood. The general objective of this book is to focus on the individual by studying intraindividual and interindividual variability in various cognitive tasks, that is, intraindividual variability across items of a given task (“inconsistency”), across various cognitive tasks (“dispersion”), and/or across years (“intraindividual change”), and of course, on interindividual differences in intraindividual variability. This book presents empirical studies that have been conducted by research groups in Europe and in North America, prominent in the field of variability and development or methodology. The 26 authors/co-authors include senior authors such as Lautrey, Schmiedek, Dauvier, van der Maas, Ghisletta, Stawski, MacDonald, and de Ribaupierre. The standard cognitive developmental approach still consists of cross-sectional studies comparing different ages. However, it has long been shown, for instance, by means of longitudinal studies, that the results are rather different when viewed from a longitudinal perspective. Moreover, there are very few studies adopting a multivariate design rather than a univariate one. As a result, we know little about intraindividual variability across tasks. The focus has systematically been on groups and not on individuals. The necessity to focus on the individual has been repeatedly emphasized, most recently in very important papers by Nesselroade and Molenaar. However, results are systematically presented based on aggregated data. Anecdotic but very illustrative can be the following statement recently read in a review: "The findings make a compelling case that intraindividual variability exists but not such a strong case that it matters. Said another way, measuring such variability often increases the testing burden on participants and researchers alike, sometimes substantially. What deep theoretical insights are likely to justify the extra effort? Many readers may conclude something like, 'Yeah, interesting, but not worth the time, effort, and cost'." This Special Issue represents a collective effort by authors coming from different geographical and theoretical horizons to convince the skeptical developmentalist that the effort is justified