Message/Author 

Jinni Su posted on Friday, September 27, 2013  1:33 pm



Hello, I want to examine a SEM model where X is hypothesized to influence Y through multiple indirect pathways that involve multiple mediators. Specifically, it is hypothesized that: X>M1>Y X>M2>Y X>M1>M3>Y X>M2>M3>Y X>M1>M2M3>Y How do I specify a model to examine all the specific indirect effects and total indirect effects of X on Y? Are the following commands correct? MODEL INDIRECT: Y IND M1 X; Y IND M2 X; Y IND M1 M3 X; Y IND M2 M3 X; Y IND M1 M2 M3 X; Y IND X; Or should I use MODEL CONSTRAINT instead? MODEL CONSTRAINT: NEW(XM1Y XM2Y XM1M3Y XM2MM3Y XM1M2M3Y); XM1Y = XM1 * M1Y; XM2Y = XM2 * M2Y; XM1M3Y = XM1 * M1M3 * M3Y; XM2M3Y = XM2 * M2M3 * M3Y; XM1M2M3Y = XM1 * M1M2 * M2M3 * M3Y; How do I obtain total indirect effects of X on Y if I use MODEL CONSTRAINT? Thanks! Jinni 


If you say MODEL INDRIECT: y IND x; you will obtain tests for all indirect effects from x to y. If this is not available, I need to know more about the scales of your variables. 

Jinni Su posted on Sunday, September 29, 2013  7:50 am



Thank you very much! I think this will work. 


I'd like to be able to do this too! But I'm new to MPlus and am wondering what to type in. I have: title: mediation; data: file = data.dat; variable: names = X M1 M2 Y; usevar = X M1 M2 Y; missing = all(999); analysis: type = general; bootstrap = 5000; output: cinterval (bcbootstrap); model: Y on M1 M2 X; M1 on X; M2 on X; MI with M2; model indirect: Y ind X 


This looks correct. Give it a try. 


I don't seem to get XM1M2Y in the output, just the two specific indirect effects separately. Am I looking in the wrong place in the output? I'm quite new to this. 


You need m2 ON m1; you have m1 WITH m2; 


Ah, thanks Prof.! I suppose if I want to add an M3 into the chain, then I would need: model: Y on M1 M2 M3 X; M1 on X; M2 on X; M3 on X; M3 on M2; M2 on M1; Is that right? 


You use an ON statement for whichever regression you want. 


I have a similar problem as above, but my model is a crosslagged panel model with 8 timepoints and I am trying to get the total effect of X at times 17 on Y at t=8 (the last one). The crosslags and autoregression only have one lag, but there are hundreds of indirect effects  too many to specify easily using Model Constraint. Is there any way of doing this using the Model Indirect command? I would also, in the next step, want to calculate the difference in this total effect between two groups (I am using latent class analysis with known classes, using Estimator = Bayes). Best, Fredrik Falkenström 


We need to see your full output with the Model Indirect request  please send your output to Mplus Support along with your license number. 


Sorry for being unclear, but my problem is that I don't know if what I want to do can be done at all. I would like to add the total indirect effects of X1 > Y8, X2 > Y8, X3 > Y8, X4 > Y8, X5 > Y8, and X6 > Y8, plus the direct effect of X7 > Y8, to get the total effect of X on Y8. As far as I know it is only possible to calculate these separately using the Model Indirect, i.e: Model Indirect: Y8 IND X1; Y8 IND X2; Y8 IND X3; etc. If I instead were to use Model Constraint, I would need to specify each and every indirect path which would take a lot of time and space, plus the risk of missing some of them. 


I don't think that sum of effects can be obtained via Model Indirect. 


Ok, I see. Is there a formula for getting the standard errors for the sum of two (or more) coefficients that I can use to calculate this afterwards? 


You can use the same Delta method approach that Model Constraint uses. I like the description in KendallStuart. The variances and covariances of parameter estimates are given in Tech3. 


Hello, I am looking to examine moderated mediation using the XWITH command, with TYPE=RANDOM. Is the only way to obtain the indirect effects with the MODEL CONSTRAINT process? Many thanks, Alex. 


Yes. 

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