ABSTRACT
This chapter presents a new, simple, and general way to express the constraints in nonlinear and interactive models of the Kenny and Judd type. Two Kenny and Judd models are implemented with the structural equation modelling program Mx. The alternative, multi-group approach to testing for moderator variables is expanded to cover the general case of continuous moderator variables, requiring a large number of groups. Mx is a software package for structural equation and other mathematical modelling. Different levels of the interaction variable are used to classify subjects into different groups. This procedure is simple to implement if the interaction variable has only a few levels, but may run foul of non-positive definite covariance matrices when the number of subjects in a group is small. More complicated nonlinear effects of a continuous Group variable might be modelled by putting Group on two consecutive paths, so that the square of the Group variable moderates the relationship.
