Factor Structure of the Intelligence and Development Scales–2: Measurement Invariance Across the Dutch and German Versions, Sex, and Age
We examined the factor structure of the intelligence and basic skills domains of the German and Dutch versions of an international test battery with 13 representative national standardizations (among others, Italian, Polish, U.K.)—the Intelligence and Development Scales–2 (IDS-2)—with confirmatory factor analyses (CFA) of the standardization samples. This included measurement invariance analyses across the Dutch and German versions and sex using multiple-group CFA, and across age using local structural equation modeling (LSEM). We tested several a priori theoretically (mostly following the Cattell–Horn–Carroll and verbal–perceptual–image rotation models) and empirically (with EFA) determined models and found a second-order model with six first-order factors best represented the Dutch IDS-2 structure. Five IDS-2 factors were confirmed, but Visual Processing and Abstract Reasoning and the intelligence and basic skills domains were not separable. This final model displayed full invariance across the Dutch and German versions and partial scalar invariance across sex, and it was largely invariant across ages 7 to 20 years. Thus, scores derived according to this final model will be comparable across these language versions, sex, and age. The strong general intelligence factor and weak broad ability factors suggest clinical interpretation should mainly be based on the full-scale IQ. We discuss the importance of testing multiple plausible models and adhering to a strict model selection procedure in CFA and implications for intelligence theory and clinical practice.