The nonlinear random coefficient model has become increasingly popular as a method for describing individual differences in longitudinal research. Although promising, the nonlinear model it is not utilized as often as it might be because software options are still somewhat limited. In this article we show that a specialized version of the model…

Twelve structural models of similarity were fitted to data from conventional and computer adaptive test (CAT) batteries measuring the same aptitude in a double cross-validation design. Three of the 12 models, including a multiplicative structure model, performed well, providing support for using CATs as replacements for conventional tests. (NSF)