Issues in the classification of mental retardation: differentiating among organic etiologies.

Many researchers of mental retardation fail to take etiological differences into account, although the value of distinguishing between organic and familial mental retardation has long been discussed. The argument is made that even the two-group approach needs to be extended so that groups with different organic etiologies are studied separately. Taking etiological distinctions into account will allow for more precise research and a better understanding of mental retardation. Evidence for the utility of differentiating retarded persons by etiology is provided by a research review showing examples of behavioral differences between organically retarded groups. It is concluded that such differentiation also has clear implications for intervention.