Applies the confluence model to a longitudinal intact family data set. Also tests the data with simple linear models. Results suggest that the confluence model should be rejected as a useful model for these data based on principles of parsimony and predictability. (Author/AS)

The paper notes A. Hore and W. Tryon's support of the developmental position that persons with and without mental retardation of similar mental age show similar cognitive patterns, but suggests that mental age is psychometrically invalid and Piagetian tasks are inappropriate to evaluate this position. An information processing approach is…