Cognitive development and individual variability

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.

Reprint of articles from the special issue published online in the open access journal "Journal of intelligence" (ISSN 2079-3200) in 2018 (available at: https://www.mdpi.com/journal/jintelligence/special_issues/cognitive_development).