Intelligence quotient scores of 4-year-old children: social-environmental risk factors.

Verbal IQ scores in a socially heterogeneous sample of 215 4-year-old children were highly related to a cumulative environmental risk index composed of maternal, family and cultural variables. Different combinations of equal numbers of risk factors produced similar effects on IQ, providing evidence that no single factor identified here uniquely enhances or limits early intellectual achievement and that cumulative effects from multiple risk factors increase the probability that development will be compromised. The multiple risk index predicted substantially more variance in the outcome measure than did any single risk factor alone, including socioeconomic status. High-risk children were more than 24 times as likely to have IQs below 85 than low-risk children.