Variation in the influence of selected sociodemographic risk factors for mental retardation.

OBJECTIVES. This study explored the utility of subdividing mental retardation into groups based on the presence of other neurological conditions. METHODS. Data were abstracted from birth certificates as part of a case-control study of mental retardation among 10-year-old children. The study sample included 458 case children and 563 control children selected from public schools. Case children were subdivided on the basis of intelligence quotient (IQ) score and the presence of other neurological conditions. RESULTS. Other neurological conditions were more common with severe mental retardation than with mild mental retardation. Regardless of IQ level or the presence of other neurological conditions, boys were more likely than girls to have mental retardation. Older mothers were more likely than younger mothers to have a child with mental retardation accompanied by another neurological condition. High birth order, Black race, and low maternal education were associated with a higher prevalence of isolated mental retardation. CONCLUSIONS. These findings suggest that sociodemographic risk factors for mental retardation vary according to the presence of other neurological conditions and that subdivisions based on medical or physical criteria may be useful in epidemiologic studies of mental retardation.