I am trying to figure out if I can use the Model Constraint function to compute a function of item parameters in an ordinal CFA model.
I have two questions: 1) Where can I find details on the operations and functions permitted in the Model Constraint command (e.g., is there a way to compute item response probabilities from a probit model)? 2) When I create a new variable using a loop, I get an estimate as a single value in the output. How is this estimate computed?
Specifically I want to to compute NCDIF, i.e., SUM (wi(F1 - F2)^2)/(SUM(wi), where F1 and F2 are logit or probit functions of the item parameters and the latent variable, and wi is the density function of the latent variable.
1) See the V8 UG pages 641-642 - all these are available also for Model Constraint, including the PHI function for probit.
2) If for instance you are using ML, the new function of the ML estimates for the parameters used in the function is in itself an ML estimate. It gets a SE and a CI. The SUM function is not available in Model Constraint.