I've heard that it is possible to test factor loading DIF in a binary CFA using nonlinear constraints. However, when I try to run the following code where lam1 is the parameter label for the factor loading and daily is the observed moderator:
model constraint: new(difl); difl=lam1*daily;
I get an error message *** FATAL ERROR THIS PARAMETER RESTRICTION MODEL IS NOT AVAILABLE. Does this mean that it is not possible to test factor loading DIF this way in Mplus or am I just specifying the DIF parameter incorrectly? I know I can use multiple group CFA to test this DIF but my goal is to ultimately test DIF for a model with 2 moderators (the binary daily variable above and another continuous variable).