Herrnstein, R.J. and Murray, C., 1994, The Bell Curve: Intelligence and Class Structure in American Life, The Free Press, New York, pp. 75-6.
SPECIFIC SKILLS VERSUS G IN THE MILITARY. The most complete data on this issue come from the armed services, with their unique advantages as an employer that trains hundreds of thousands of people for hundreds of job specialties. We begin with them and then turn to the corresponding data from the civilian sector.
In assigning recruits to training schools, the services use particular combinations of subtests from a test battery that all recruits take, the Armed Services Vocational Aptitude Battery (ASVAB). The Pentagon’s psychometricians have tried to determine whether there is any practical benefit of using different weightings of the subtests for different jobs rather than, say, just using the overall score for all jobs. The overall score is itself tantamount to an intelligence test. One of the most comprehensive studies of the predictive power of intelligence tests was by Malcolm Ree and James Earles, who had both the intelligence test scores and the final grades from military school for over 78,000 air force enlisted personnel spread over eighty-nine military specialties. The personnel were educationally homogeneous (overwhelmingly high school graduates without college degrees), conveniently “controlling” for educational background. What explains how well they performed? For every one of the eighty-nine military schools, the answer was g— Charles Spearman’s general intelligence. The correlations between g alone and military school grade ranged from an almost unbelievably high .90 for the course for a technical job in avionics repair down to .41 for that for a low-skill job associated with jet engine maintenance. Most of the correlations were above .7. Overall, g accounted for almost 60 percent of the observed variation in school grades in the average military course, once the results were corrected for range restriction…
Did cognitive factors other than g matter at all? The answer is that the explanatory power of g was almost thirty times greater than of all other cognitive factors in ASVAB combined. The table below gives a sampling of the results from the eighty-nine specialties, to illustrate the two commanding findings: g alone explains an extraordinary proportion of training success; “everything else” in the test battery explained very little.