Sex differences in cognitive abilities: Analyses for the German WAIS-IV

- There are substantial sex effects in favor of males in cognitive abilities as measured by the German WAIS-IV.
- Effect sizes for sex differences are considerably lower than those for differences regarding educational level.
- Sex effects do not depend on educational level (no interaction).
- In order to decide on the need of sex-specific norm tables future research must elucidate the nature of sex differences: bias or genuine effect?

Sex differences on 15 subtests, the four indices, and the full scale IQ of the Wechsler Adult Intelligence Scale - Fourth Edition (WAIS-IV) are examined in the total national standardization sample (N = 944 males, 924 females) of the WAIS-IV. This sample, whose ages range from 16 to 89 years, were chosen by a stratified, random-sampling procedure to be representative of the population of Germany according to demographic features revealed in the 2012 census. Women scored lower in all indices and subtests with the exception of the Processing Speed Index (PSI) and the associated subtests, whereby the differences in means range between 3.2 and 4.9 IQ-points at the index level (FSIQ: Difference = 3.2, WMI: Difference = 4.9). But the maximum effect size of sex tends to be smaller (η2 = 0.050) than the minimum effect size of education level (ranges from ω2 = 0.055 to ω2 = 0.289). It must be noted that the participants' education background, as defined by the highest attained education level, exerted a much greater effect upon cognitive abilities than sex did. A psychobiosocial model with the aim of accounting for sex-related differences in intelligence should be discussed.