Bell Curve

286 The National Context Ethnic Differences in Cognitive Ability 287and white differences in test scores and performance measures. The hypothesismight, in theory, be true. But given the degree to which everydayexperience suggests that the environment confronting blacks indifferent sectors of American life is not uniformly hostile and given theconsistency in results from a wide variety of cognitive measures, assumingthat the hypothesis is true represents a considerably longer leap offaith than the much more limited assumption that race prejudice is stilla factor in American life. In the matter of test bias, this brings us to thefrontier of knowledge.Are the Differences in Overall Black and White Test Scores Attributableto Difieerences in Socioeconomic Status?This question has two different answers depending on how the questionis understood, and confusion is rampant. We will take up the two answersand their associated rationales separately:First version: If you extract the effecn of socioeconomic clars, what happensto the overall magnitude of the BIW difference? Blacks are disproportionatelyin the lower socioeconomic classes, and socioeconomic classis known to be associated with IQ. Therefore, many people suggest, partof what appears to be an ethnic difference in IQ scores is actually a socioeconomicdifference.The answer to this version of the question is that the size of the gapshrinks when socioeconomic status is statistically extracted. The NLSYgives a result typical of such analyses. The B/W difference in the NLSYis 1.21. In a regression equation in which both race and socioeconomicbackground are entered, the difference between whites and blacksshrinks to .76 standard deviation.lW1 Socioeconomic status explains 37percent of the original B/W difference. This relationship is in line withthe results from many other ~tudies.'~"The difficulty comes in interpreting what it means to "control" forsocioeconomic status. Matching the status of the groups is usually justifiedon the grounds that the scores people earn are caused to some extentby their socioeconomic status, so if we want to see the "real" or"authentic" difference between them, the contribution of status mustbeThe trouble is that socioeconomic status is also a resultof cognitive ability, as people of high and low cognitive ability move tocorrespondingly high and low places in the socioeconomic continuum.The reason that parents have high or low socioeconomic status is in parta function of their intelligence, and their intelligence also affects theIQ of the children via both genes and environment.Because of these relationships, "controlling" for socioeconomic statusin racial comparisons is guaranteed to reduce IQ differences in thesame way that choosing black and white samples from a school for theintellectnally glfted is guaranteed to reduce IQ differences (assumingrace-hlind admissions standards). But the remainmg difference is notnecessarily more real or authentic than the one we start with. This seemsto he a hard point to grasp, judging from the pervasiveness of controllingfor socioeconomic status in the sociological literature on ethnic differences.Rut suppose we were asking whether blacks and whites differedin sprinting speed, and controlled for "varsity status" by examining onlyathletes on the track teams in Division I colleges. Blacks would probablystill sprint faster than whites on the average, but it would be a smallerdifference than in the population at large. Is there any sense in whichthis smaller difference would be a more accurate measure of the racialdifference in sprinting ability than the larger difference in the generalpopulation? We pose that as an interesting theoretical issue. In terms ofnumhers, a reasonable rule of thumb is that controlling for socioeconomicstatus reduces the overall B/W difference hy about a third.Second version: As blacks move up the socioecnnomic ladder, do the differenceswith whites of similar socioeconomic status diminish? The first versionof the SESIIQ question referred to the overall score of a populationof blacks and whites. The second version concentrates on the B/W differencewithin socioeconomic classes. The rationale goes like this:Blacks score lower on average because they are socioeconomically at adisadvantage in our society. This disadvantage should most seriouslyhandicap the children of blacks in the lower socioeconomic classes, whosuffer from greater barriers to education and occupational advancementthan do the children of blacks in the middle and upper classes. As blacksadvance up the socioeconomic ladder, their children, less exposed tothese environmental deficits, will do better and, by extension, close thegap with white children of their class.This expectation is not borne out by the data. A good way to illustratethis is by using our parental SES index and matching it against themean IQ score, as shown in the figure below. 1Q scores increase witheconomic status for both races. But as the figure shows, the magnitudeof the B/W difference in standard deviations does not decrease. Indeed,it gets larger as people move up from the very bottom of the socioeco-