Life-span development of institutionalized and community-based mentally retarded persons, revisited.

Life-span development of adaptive behavior of 30,749 mentally retarded individuals residing in California and being served by the California Department of Developmental Services was studied. The estimated life-span trends differed somewhat from those reported in an earlier investigation (Eyman & Arndt, 1982.) We used a larger sample and a more appropriate model and found different growth curves in adaptive behavior over levels of retardation, contrary to the Eyman and Arndt findings. Moreover, when cross-sectional vs. semi-longitudinal growth curves were compared, the degree of similarity of the two types of curves was a function of level of retardation. Evidence on the need for large sample life-span studies based on at least 6 to 8 years follow-up was presented.