How useful are specific cognitive ability scores? An investigation of their stability and incremental validity beyond general intelligence

Many intelligence tests measure multiple specific cognitive abilities. Practitioners use these specific ability scores, which encompass both specific ability and general intelligence variance, and the resulting intelligence profiles to make counseling and intervention decisions. In the present study, we investigated the temporal stability of eight specific abilities and their profiles over one school year, as well as their incremental validity in the prediction of school grades with German grade 7 to 9 students (N = 326 at T1; N = 311 at T2; N = 257 with IQ data at both times of measurement). The mean rank-order stability was 0.80 and ranged from 0.71 to 0.85. Intelligence profiles replicated significantly above chance levels (Mdn_κ = 0.31). The incremental validity coefficients were mostly small, but the Reasoning score substantially contributed to the prediction of math grades (ΔR² = 0.07–0.09), the Verbal Ability score to the prediction of German grades (ΔR² = 0.05–0.09), and the Crystallized Intelligence score to the prediction of geography grades (ΔR² = 0.03–0.08) beyond the general intelligence score. Our study of specific ability scores indicated moderate to high rank-order stability, fair to moderate profile stability, and substantial incremental validity for some specific ability scores.