Bell Curve

134 Cognitive Classes and Social Behavior Poverty 13 5The comparative roles of IQ and parental SES in determiningwhether young white adults are below the poverty lineProbability of being in poverty30% -:\As IQ goes from low to high,As parental SES goes- from low to highVery low(-2 SDs)Note: For computing the plot, age and either SES (for the hlack curve) or 1Q (for the graycurve) were set at their mean values.population). Look at the far left-hand part of the graph. Now, our imaginaryperson with an average socioeconomic background has about a 26percent chance of being in poverty. The gray line lets you ask, "Imaginea person in the NLSY who is exactly average in IQ and age. Whatare this person's chances of being in poverty if he came from an extremelyadvantaged socioeconomic background? An extremely de-IRefresher112 standard deviation below and above the mean cuts off the 31st and69th percentiles. A 112 SD difference is substantial.1 standard deviation below and above the mean cuts off the 16th and84th percentiles. A 1 SD difference is big.2 standard deviations below and above the mean cuts off the 2d and98th percentiles. A 2 SD difference is very big.A "standard score" means one that is expressed in terms of standard deviations.prived socioeconomic background!" As the gray line indicates, the prohabilityof being in poverty rises if he was raised by parents who were lowin socioeconomic status , but only gradually.In general, the visual appearance of the graph lets you see quickly theresult that emerges from a close analysis: Cognitive ability is more importantthan parental SES in determining poverty."3'This does not mean that socioeconomic background is irrelevant.The magnitude of the effect shown in the graph and its statistical regularitymakes socioeconomic status significant in a statistical sense. Toput it into policy terms, the starting line remains unequal in Americansociety, even among whites. On the other hand, the magnitude of thedisadvantage is not as large as one might expect. For example, imaginea wh~te person born in 1961 who came from an unusually deprived socioeconomicbackground: parents who worked at the most menial ofjobs, often unemployed, neither of whom had a high school education(a description of what it means to have a socioeconomic status indexscore in the 2d centile on soc~oeconomiclass). If that person ha. an IQof 100-nothing special, just the national average-the chance offalling below a poverty-level income in 1989 was 11 percent. It is notzero, and it is not as small as the risk of poverty for someone from a lesspunishing environment, but in many ways this is an astonishing statementof progress. Conversely, suppose that the person comes from the2d centile in IQ but his parents were average in socioeconomic statuswhichmeans that his parents worked at skilled jobs, had at least finishedhigh school, and had an average income. Despite coming fromthat solid background, his odds of being in poverty are 26 percent, morethan twice as great as the odds facing the person from a deprived homebut w~th average intelligence.In sum: Low intelligence means a comparatively high risk of poverty.If a white child of the next generation could be given a choice betweenbeing disadvantaged in socioeconomic status or disadvantaged in intelligence,there is no question about the right choice.EducationNow let us consider whether education really explains what is going on.One familiar hypothesis is that if you can only get people to stick withschool long enough, they will be able to stay out of poverty even if theyhave modest test scores.As in subsequent chapters, we will consider two educational groups: