I am running a twolevel CFA (4 factors, 22 variables; ordinal data, WLSMV estimator) examining model fit for an unconstrained (Ho) and constrained (Ha) model (factor loading invariance across levels).
All my reading indicates using the DIFFTEST procedure to compare nested models when using the WLSMV estimator.
However, placing the DIFFTEST option in the SAVEDATA command when estimating the Ha model generates an error message:
"The DIFFTEST option is not available for TYPE=TWOLEVEL. Request for DIFFTEST will be ignored."
I am following the 2-step process describe in the MPLUS manual (p.625; 2012 edition) for applying DIFFTEST with the WLSMV estimator .
I assume from the message I cannot use a DIFFTEST option method because it is a TWOLEVEL model, and I will need to compute the test statistic manually. Is there a reference for how use the output from my Ho & Ha models to do this?