Investigating measurement invariance of the IDS-2 intelligence scales between migrant and non-migrant groups

Intelligence plays a crucial role in various aspects of human life, impacting health, academic achievement, and socio-economic success. However, cultural and linguistic disparities in intelligence testing pose challenges, particularly for individuals from migrant backgrounds. This study replicates and extends the landmark study by Wicherts and Dolan (2010) exploring measurement invariance of the German language intelligence test, the Intelligence and Development Scales – 2 (IDS-2), between children and adolescents from migrant (N = 132) and non-migrant (N = 1898) groups. The results revealed partial strict measurement invariance in the IDS-2 intelligence scale subtests across the examined groups. The breach of full strict measurement invariance is primarily due to intercept differences on the verbally loaded subtests—Naming Categories, Naming Opposites, and Story Recall—highlighting the confounding impact of language complexity on test outcomes. These discrepancies resulted in a cumulative intercept difference disadvantaging migrant participants of approximately 4 IQ points on the Full-Scale IQ Score. The findings indicate that while the IDS-2 scales generally assess intelligence consistently across diverse groups, the influence of language complexity on the verbal subtests may result in a disadvantage for children and adolescents with migration backgrounds. To address these biases, we propose the development of non-verbal and culturally fair intelligence tests.