Family Size and Birth order as Factors on the IQ Performance of Black and white Children

Originally developed by Zajonc and Markus (1975), the confluence model attempts to explain the intellectual growth of children as a function of the family structures in which children are reared. Using data extracted from Cycle II of ihe National Health Examination Survey, we analyze the effects of two of the most frequently investigated indicators offamily structure; the number of siblings and birth-order on the Wechsler vocabulary and the Wechsler block design (IQ sub-tests) performance of 6 to 11-year-old children. The effects of these family structure variables on IQ performance are estimated for black and white children. Four major conclusions are drawn. First, birth-ordkr is unrelated to the verbal and nonverbal IQ performance of either black or white children. Second, family size is inversely related to the verbal IQ performance of black and white children but not to the nonverbal performance of either group. Third, the inverse impact of family size on verbal ability does not differ significantly by race. Finally, the only child exception to the family sizelIQ linear decline frequently reported in other studies is not supported in this study for the IQ performance of black children and it is barely supported for the IQ performance of white children appearing only and slightly on the vocabulary sub-test.