Measurement Invariance of the Intelligence and Development Scales-2 Across Language Versions, Gender, and Age

We examined the factor structure and measurement invariance of the intelligence and basic skills domains of the Intelligence and Development Scales - 2 (IDS-2) with the Dutch (N = 1,665) and German (N = 1,672) standardization samples. First, we tested five competing models using confirmatory factor analysis (CFA) on the Dutch data: two empirically based, derived earlier from the German data, and three theoretically based (IDS-2 and two Cattell-Horn-Carroll-based). Subsequently, we evaluated the measurement invariance of the final model across the Dutch and German versions and gender using multiple-group CFA and across age using local structural equation modeling. 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 model displayed full invariance across the language versions and was largely invariant across gender and age (7-20 years). Thus, scores derived according to this model are comparable across these language versions, gender, and age. The strong general intelligence factor and weak broad ability factors ask for precaution when basing clinical interpretation on the broad ability factors.