GxD test but, more importantly, they do not allow for the measure of individual change. That is, a cross-sectional approach with two samples of different ages would allow between-group tests but not change at the individual level (Curran & Bauer, 2011). Longitudinal studies are preferred, but they require specialized statistical methods that account for developmental change nested within subject (for a review of methods in longitudinal analysis of behavior, see (Curran & Bauer, 2011; Gibbons, Hedeker, & DuToit, 2010))
