Hi, We are attempting to test 2-1-1 mediation using DSEM and could use some guidance on code construction. We are using time-varying EMA data on mood and smoking for m and y. X is a time-invariant measure of SES for 375 participants.
My primary question is what it means for interpreting the ab path to also have y on m estimated at the Between level in DSEM. Preacherís 2-1-1 models have this path whereby the within b path is added to the between b path before multiplying ab. Thanks so much.
%WITHIN% s_my | y on m; ! L1 b path phi | y on y&1; ! L1 control for autoreg y m; ! L1 residual variances
%BETWEEN% x m y; ! L2 residual variances s_my WITH phi y m; ! covariances phi WITH y m; y WITH m;
[phi]; ! L2 autoreg mean [s_my] (bw); ! L2 b path mean y on x (c); m on x (a);
If you are using DSEM then you need to understand the sentence containing equation (61) in http://statmodel.com/download/DSEM.pdf From there using plausible values you need to compute bw=E(s_my/(1-phi)). That is the only way unfortunately such an expectation is generally undefined for two normal random effects.
In the next Mplus version we will have some of these steps simplified.
A great first step would be to simplify the model by replacing
phi | y on y&1;
y on y&1 (phi);
In many case Var(phi) is too small anyway so it would not be detrimental to assume the same autocorrelation across subjects. In that case the indirect effect is simplified substantially and you can simply use