Shouldn’t Spearman’s hypothesis have graduated to the level of theory by now?
Periodically, researchers claim to have developed an alternative general cognitive ability (g) test that assesses g but exhibits lower than typically found mean racial differences. To the extent that such measures have reduced mean racial differences, we argue that they have less g saturation (i.e., they measure g less well) and will have lower validity and larger prediction errors than tests with high g saturation. Using a sample of 22,728 people from the General Aptitude Test Battery database, we show that one can decrease mean racial differences in a g test by altering the g saturation of the test. Consistent with Spearman’s Hypothesis, the g saturation of a test is positively, and strongly, related to the magnitude of White-Black mean racial differences in test scores. We demonstrate that the reduction in mean racial differences accomplished by reducing g saturation in a test is obtained at the cost of lower validity and increased prediction errors. We recommend that alternative g tests be evaluated in comparison to highly g saturated tests with respect to Spearman’s Hypothesis, test validity, and prediction errors