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Jinni Su posted on Friday, September 27, 2013 - 1:33 pm
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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 |
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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. |
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Jinni Su posted on Sunday, September 29, 2013 - 7:50 am
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Thank you very much! I think this will work. |
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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 |
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This looks correct. Give it a try. |
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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. |
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You need m2 ON m1; you have m1 WITH m2; |
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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? |
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You use an ON statement for whichever regression you want. |
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I have a similar problem as above, but my model is a cross-lagged panel model with 8 time-points and I am trying to get the total effect of X at times 1-7 on Y at t=8 (the last one). The cross-lags 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 |
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We need to see your full output with the Model Indirect request - please send your output to Mplus Support along with your license number. |
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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. |
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I don't think that sum of effects can be obtained via Model Indirect. |
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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? |
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You can use the same Delta method approach that Model Constraint uses. I like the description in Kendall-Stuart. The variances and covariances of parameter estimates are given in Tech3. |
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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. |
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Yes. |
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Cheng posted on Monday, October 05, 2020 - 1:32 am
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There is a reciprocal relationship in my SEM model. When I use Model Indirect command, Mplus output only provides Total, Total indirect. However, it doesn't provide Specific indirect and Direct effect. Is there any reason for this? |
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Yes - there are infinitely many paths. You can get specific effects using the specific effects command y1 ind y2 y3; See page 762 in the User's Guide. |
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Cheng posted on Thursday, October 08, 2020 - 12:11 am
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There is no difference if I use y1 VIA y2 y3 or y1 IND y2 y3 is that right? |
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Use VIA. |
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