Capturing age-group differences and developmental change with the BASC Parent Rating Scales

•We show the need to maximize test–content parallelism in applied developmental studies.•We compare the level of measurement invariance reached with parallel vs. non-parallel scales.•We estimate biases resulting from using non-parallel scales for two age groups.•Only scales with parallel content hold a level of invariance proper for developmental studies.

Estimation of age-group differences and intra-individual change across distinct developmental periods is often challenged by the use of age-appropriate (but non-parallel) measures. We present a short version of the Behavior Assessment System (Reynolds & Kamphaus, 1998) Parent Rating Scales for Children (PRS-C) and Adolescents (PRS-A), which uses only their common-items to derive estimates of the initial constructs optimized for developmental studies. Measurement invariance of a three-factor model (Externalizing, Internalizing, Adaptive Skills) was tested across age-groups (161 mothers using PRS-C; 200 mothers using PRS-A) and over time (115 mothers using PRS-C at baseline and PRS-A five years later) with the original versus short PRS. Results indicated that the short PRS holds a sufficient level of invariance for a robust estimation of age-group differences and intra-individual change, as compared to the original PRS, which held only weak invariance leading to flawed developmental inferences. The importance of test–content parallelism for developmental studies is discussed.