Bell Curve

80 The Emergence of a Cognitive Elite The Economic Pressure to Partition 81sure of ability and grade point average is used as the measure of achievement,33Students with differing SATs sometimes differ more in theirfreshman grades than in later years. That is why President Bok grantedpredictive value to the SAT only for first.year grades.34 On the otherhand, the shrinking predictive power may be because students learnwhich courses they are likely to do well in: They drop out of physics orthirddyear calculus, for example, and switch to easier courses. They findout which professors are stingy with A's and B's. At the U.S. MilitaryAcademy, where students have very little choice in courses, there is noconvergence in grades.35When it comes to job performance, the balance of the evidence isthat convergence either does not occur or that the degree of convergenceis small. This was the finding of a study of over 23,000 civilianemployees at three levels of mental ability (high, medium, and low), usingsupervisor ratings as the measure of performance, and it extendedout to job tenures of twenty years and more.36 A study of four militaryspecialties (armor repairman, armor crewman, supply specialist, cook)extending out to five years of experience and using three different measuresof job performance (supervisor's ratings, work sample, and jobknowledge) found no reliable evidence of ~onver~ence.~' Still anothermilitary study, which examined several hundred marines working as radiorepairmen, automotive mechanics, and riflemen, found 110 convergenceamong personnel of differing intelligence when job knowledgewas the measure of performance but did find almost complete convergenceafter a year or so when a work sample was the mea~ure.~'Other studies convey a similarly mixed picture.[391 Some experts areat this point concluding that convergence is uncommon in the ordinaryrange of jobs.[401 It may be said conservatively that for most jobs, basedon most measures of productivity, the difference in productivity associatedwith differences in intelligence diminishes only slowly and partially.Often it does not diminish at all. The cost ofhiring less intelligentworkers may last as long as they stay on the job.TEST SCORES COMPARED TO OTHER PREDICTORS OFPRODUCTIVITYHow good a predictor of job productivity is a cognitive test score comparedto a job interview? Reference checks! College transcript? The an-swer, probably surprising to many, is that the test score is a better predictorof job performance than any other single measure. This is theconclusion to be drawn from a meta-analysis on the different predictorsof job performance, as shown in the table below.The Validity of Some Different Predictorsof Job PerformancePredictorValidity Predicting JobPerformance RatingsCognitive test score .53Biographical data .37Reference checks -26Education .22Interview .14College grades .I1Interest .10Age -,01Source: Hunter and Hunter 1984.The data used for this analysis were top heavy with higher-complexityjobs, yielding a higher-than-usual validity of .53 for test scores. However,even if we were to substitute the more conservative validityestimate of .4, the test score would remain the best predictor, thoughwith close competition from biographical data4' The method that manypeople intuitively expect to be the most accurate, the job interview, hasa poor record as a predictor of job performance, with a validity ofonly .14.Readers who are absolutely sure nonetheless that they should tmsttheir own assessment of people rather than a test score should pause toconsider what this conclusion means. It is not that you would select amarkedly different set of people through interviews than test scoreswould lead you to select. Many of the decisions would be the same. Theresults in the table say, in effect, that among those choices that wouldbe different, the employees chosen on the basis of test scores will on averagebe more productive than the employees chosen on the basis of anyother single item of information.