[Various familial and demographic indicators in relation to the severity of mental retardation in the probands].

A comparative analysis was made of some familial and demographic characteristics in 3 groups of mentally retarded patients with varying intensity of deficiency. The hypothesis of different etiology of mild and severe mental retardation was confirmed. Appreciable differences were found in the microsocial characteristics in the intermediate group of patients with marked debility. In certain characteristics, this group was similar to the gravest patients whereas in some others, to the group with mild grades of intellectual underdevelopment. This fact can be accounted for by the heterogeneity of the intermediate group.