Poverty Lowers IQ, Study Says

Adjustments for socioeconomic conditions almost completely eliminate differences in IQ scores between black and white children, according to the study's co-investigators. They include Jeanne Brooks-Gunn and Pamela Klebanov of Columbia's Teachers College, and Greg Duncan of the Center for Urban Affairs and Policy Research at Northwestern University.

As in many other studies, the black children in the study had IQ scores a full 15 points lower than their white counterparts. Poverty alone, the researchers found, accounted for 52 percent of that difference, cutting it to 7 points. Controlling for the children's home environment reduced the difference by another 28 percent, to a statistically insignificant 3 points -- in essence, eliminating the gap altogether.

"The study strongly suggests that economic and learning environments of the home are the most powerful predictors of racial IQ differences in 5-year-olds," said Brooks-Gunn.

The longitudinal data allowed the researchers to measure persistent poverty -- found to be a key factor in the IQ differences. "Many children have transitory experiences with poverty," said Duncan. "For black children, poverty is likely to be much more persistent," he said. Of the black children in the study, 40 percent lived in persistent poverty, compared to 5 percent of white children.

The study also takes into account how impoverished neighborhood conditions and environmental influences can affect even children not living in poverty. Black families are more likely to live in poor neighborhoods, whether or not they are poor themselves. "Almost one half of all black children whose families were not poor resided in poor neighborhoods, compared with less than 10 percent of white children," said Duncan.

In addition, the study measured other factors associated with poverty that are more common in minority children. They include characteristics related to family structure and resources: single parents, parents with low educational levels and low literary scores, unemployed parents and young parents.

To determine the child's level of stimulation in the home environment, the data included measurements of parents' involvement and learning and language experiences that they provided for their children. For example, it measured whether the child has toys that teach color, size and shape and whether the child is encouraged to learn the alphabet and numbers.

The Bell Curve hypothesis does not depend on any direct evidence, but rather on its authors' assertion that social and economic factors cannot explain it. Because the typical black ranks at the 15th percentile of the white IQ distribution, say Hernstein and Murray, black socioeconomic status (SES) can only explain the ranking if, on average, it is well below than the 15th percentile of white SES ranking.

The Bell Curve authors claim no such SES inequality exists, and this is the point the Columbia-Northwestern study calls into question. Most studies of socioeconomic status do not consider such obvious factors as family income or neighborhood conditions, and those that do fail to account for the degree of persistent poverty.

Three times as many black children as white children live in families below the official U.S. poverty line. The average black child in the United States lives in a family whose long-term income ranks at about the ninth percentile of white income distribution, according to the study. The percentile ranking for blacks drops to about the fifth percentile of white income distribution when adjusted for the very different neighborhood conditions black and white children typically live in.

The significance of these factors, and the consequent finding that the economic and learning environments of the home are the most powerful predictors of age-5 racial IQ differences, is the implication that the debate spawned by "The Bell Curve" has badly misdirected the national debate on welfare reform.

Such reform is clearly needed, said Duncan, Brooks-Gunn and Klebanov, but the point of reform should be to focus on the real problems of children rather than the presumed moral failings of their parents. Whatever the merits of requiring mandatory employment and responsible behavior, the researchers said, the key issue -- and the one with the greatest impact on the nation's future -- is how such requirements will affect family poverty.