I am looking for some help using Mplus trying to do a longitudinal mediation. My study involved taking pre-post measurements of several variables as part of an intervention that had two groups; a control group and a treatment group.
I need the mediator and outcome variables to be change scores and I am uncertain how to tell Mplus to interpret the mediator and outcome variables as change scores in the Define category . My model has the correct syntax to create the change scores , I just don’t know how to tell Mplus to use the change score variable as the mediator and outcome variable.
I have missing data for the post measurements as several people dropped off during the study. However I am doing an intent-to-treat analysis. Do I need to add anything on the syntax to account for this? I am already specifying that values with -999 are missing and I am also using the ML estimator.
Do I need to rename it somehow?
Any help is much appreciated.
DATA: FILE IS Organized Full Sheet.dat;
ActiveC !ActiveC is a binary categorical independent variable
NGSE NGSEA !New General Self Efficacy Scale; complete in NGSA and
DIET DIETA !about 50% on DIETA.
Wght WghtA; !Weight variable; complete in Wght and about 47% in WghtA.
usevariables NGSE NGSEA Wght WghtA X M Y;
missing = all ;
X = ActiveC;
M = NGSA – NGS;
Y = WghtA – Wght;
TYPE = GENERAL;
ESTIMATOR = ML;
BOOTSTRAP = 10000;
NGSEA ON NGSE@1;
delta by NGSEA@1;
delta with NGSE;
Wghta ON Wght@1;
delta by Wghta@1;
delta with Wght;
Y ON M ;
Y ON X ;
M ON X ;
a1b1 = a1*b1;
TOTAL = a1*b1 + cdash;
STAND CINT ;