Commentary: On the importance of looking at nonlinearity and developmental effects - a reflection on Flom et al....

By examining both linear and curvilinear associations between mental development and activity level, the study by Flom et al. (Journal of Child Psychology and Psychiatry, 2017) highlights the importance of going beyond linear associations in psychological fields of research. Results from Flom et al. (Journal of Child Psychology and Psychiatry, 2017) also raise interesting questions for future research. First, studies should look at variables that may explain the associations between activity level and mental development, such as self-regulation and attention. Second, longitudinal changes in the strength of the association between activity level and mental development should be examined to determine when this association is at its strongest. Finally, longitudinal research looking at bidirectional effects is needed to confirm the direction of the associations between activity level and mental development. Answers to these questions will allow the identification of the best targets and developmental periods for interventions to take place.