An Evaluation of Spearman’s Hypothesis by Manipulating g Saturation Michael A. McDaniel and Sven Kepes Department of Management, Virginia Commonwealth University, 301 West Main Street, PO Box 844000, Richmond, VA 23284-4000, USA. mamcdani@vcu.edu Spearman’s Hypothesis holds that the magnitude of mean White–Black differences on cog- nitive tests covaries with the extent to which a test is saturated with g. This paper evaluates Spearman’s Hypothesis by manipulating the g saturation of cognitive composites. Using a sample of 16,384 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 meas- ure. 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 the g saturation in a measure is obtained at the cost of lower validity and increased predic- tion errors. We recommend that g tests varying in mean racial differences be examined to determine if the Spearman’s Hypothesis is a viable explanation for the results. 1. Introduction T wo questions periodically reappear in the personnel selection literature: (1) what causes one cognitive ability test to be more predictive of job performance than another and (2) what causes one cognitive ability test to have smaller mean racial differences than an- other. Regarding the first question, scientific evidence indicates that the validity of a cognitive test is largely a function of the extent to which the test measures g (Gottfredson, 2002; Olea & Ree, 1994; Ree, Earles, & Teachout, 1994; Sackett, Schmitt, Ellingson, & Kabin, 2001; Schmidt, 2002; Thorndike, 1986). Spearman is credited with identifying a general factor of intelligence (g) that could be derived from any broad set of cognitive measures (Spearman, 1904, 1927), and the research stream began by Spearman is often labeled as the ‘psy- chometric g’ literature. The second question was di- rectly addressed by Spearman (1927, p. 379), who noted that the magnitude of mean White–Black differences covaried with the extent to which a test was ‘saturated with g.’ This positive relationship between the g satura- tion of tests and the magnitude of the tests’ White– Black mean differences became known as ‘Spearman’s Hypothesis.’ Jensen (1985, 1998) reviewed many studies supporting Spearman’s Hypothesis. Thus, to accept Spearman’s Hypothesis is to adopt the position that one cannot develop a g test that measures g well (i.e., a test that has a high g saturation) and has low White–Black mean differences. Typically, studies concerning Spearman’s Hypothesis examine intact test composites for the relation between g saturation and the mean racial differences of the tests comprising the composite. In this study, we take a dif- ferent approach. We manipulate a 9-scale test compos- ite to create multiple measures (composites) that vary in g saturation. We evaluate Spearman’s Hypothesis by examining how mean Black–White score differences covary with g saturation. In addition, we also consider how differences in g saturation affect criterion-related validity and prediction errors. Differences across the composites cannot be attributed to sample differences because all composites are based on data from the same sample. Furthermore, because we are manipulating the g saturation of the composites, we can have greater con- fidence that the observed effects are due to g saturation and not other factors. In addition, we use two ap- proaches to alter the g saturation of the composites to evaluate whether our results are due to a particular method. Thus, we offer these analyses as a unique ap- proach to evaluating Spearman’s Hypothesis and argue that it represents a unique contribution to the Spear- International Journal of Selection and Assessment Volume 22 Number 4 December 2014 © 2014 John Wiley & Sons Ltd, 9600 Garsington Road, Oxford, OX4 2DQ, UK and 350 Main St., Malden, MA, 02148, USA