I am conducting a multilevel mediation SEM with random intercepts and fixed slopes. However, a reviewer of my current paper suggested to test for random slopes and to groupmean center the predictor variable. Unfortunately, I think it is not possible to test for random slopes without montecarlo integration (and I really don't know how to use this) and the models I tried previously couldn't be computed due to low memory capacity. I also don't know how to groupmean center a latent variable in Mplus.
This is an extract of my current model in Mplus 8.4:
ANALYSIS: type=twolevel; estimator=ML;
Model: %within% f1w by item1 item2 item3 item4; f2w BY item1 item2 item3; f3w BY item1 item2 item3;
f2w ON f1w; f3w ON f1w f2w;
%between% f1b by item1 item2 item3 item4; f2b BY item1 item2 item3; f3b BY item1 item2 item3;
f2b ON f1b; f3b ON f1b f2b;
MODEL INDIRECT: f3w IND f1w;
My questions are: 1. How can I test if the slopes of the particular effects are random? 2. How can I groupmean center the predictor variable f1w?
The memory requirement is a function of the number of dimensions of integration and the sample size. To guide you, you need to send your data output with random slopes - along with your license number.