What is constrained LCA?
With constrained LCA, one places restrictions on the allowable values of estimated model parameters. Constraints may be of three types: • Fixed value constraints restrict the values of parameters to certain values. For example, one may require that the probability of a positive or “yes” response to a certain item be .90 for a certain latent class. • Equality constraints restrict two or more parameters to have equal values. For example, one may require that the probability of a “yes” response for two or more items be identical in a given latent class. • Structural parameter constraints are more complex. These involve functions that affect the values of two or more parameters simultaneously (See FAQ, What are discrete latent trait models?). Structural constraints can also used for LCA with ordered-category data. Formann (1985) and others have described logistic latent class models that can be applied to a wide variety of problems. Croon (1990; 1991) described structural constraints in co
