MODEL INDIRECT or MODEL CONSTRAINT?
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-->M2--M3-->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
 Linda K. Muthen posted on Saturday, September 28, 2013 - 6:39 am
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.
 Jonathan Jong posted on Saturday, May 10, 2014 - 8:54 am
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
 Linda K. Muthen posted on Saturday, May 10, 2014 - 11:21 am
This looks correct. Give it a try.
 Jonathan Jong posted on Saturday, May 10, 2014 - 2:49 pm
I don't seem to get X-M1-M2-Y 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.
 Linda K. Muthen posted on Saturday, May 10, 2014 - 5:22 pm
You need

m2 ON m1;

you have

m1 WITH m2;
 Jonathan Jong posted on Sunday, May 11, 2014 - 1:00 am
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?
 Linda K. Muthen posted on Sunday, May 11, 2014 - 7:01 am
You use an ON statement for whichever regression you want.
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