A test of Spearman's 'Law of Diminishing Returns' in two large samples of Danish military draftees

摘要

Spearman's "Law of Diminishing Returns" (SLODR) predicts that g saturation for cognitive tests will be lower at high ability levels than at low ability levels. This hypothesis was tested in two large samples of Danish military draftees (n=33,833 and n=25,020). The subjects were representative samples of the young adult male population and 95% were aged 18–19. Both samples were tested with a group intelligence test comprised of four subtests which was used to form high and low ability groups within each sample. The g saturation of the battery was estimated within each group using the average intercorrelation and the total explained variance of the first principal component (PC1) and first factor from a principal axis factoring (PAF1). Two different cutoff points were used to illustrate the effect of difference in standard deviation (S.D.) for subtest and total ability score. For both samples and for both cutoff points, SLODR could not be confirmed. In fact, support was found for the opposite effect, namely, a higher g saturation for the high ability group as compared to the low ability group. Furthermore, SLODR may be dependent upon the cutoffs used to define ability groups and also the number and overall g loading of the cognitive tests used.