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Apologies in advance if this is a repeat posting, my system hiccupped a while ago and I lost track of my posting. I am trying to model a mediation model in which a X is a binary predictor (treatment vs. control), M is a mediator (continuous), and Y is a Binary outcome. I am interested in the indirect effect of X on Y as it passes through M. My syntax and ensuing error are shown below: title: Mediation Dichotomous data: file= 'C:\test.txt'; variable: names=X M Y; USEVARIABLES ARE X M Y; CATEGORICAL ARE Y X; MODEL: Y ON X; Y ON M X; MODEL INDIRECT: Y VIA M X; ERROR: *** ERROR in Variable command CATEGORICAL option is used for dependent variables only. X is not a dependent variable. 


The CATEGORICAL option is for dependent variables. The variable x is an independent variable. You should take x off of the CATEGORICAL list. The scale of independent variables does not affect model estimation. 


Linda, Thanks, for the clarification on how to state the measurement quality of the variables. I'd like to continue this line with a more simple question about how to create my model. How do I estimate a mediation model in which the effects of X on Y are mediated by M, and in which X and Y are binary? (I see from you earlier comment that I do not declare X as binary.) I want to obtain the estimates of the indirect effects of X on Y through M and the SE of the indirect estimate? In this model the regression of M on X is a linear regression and Y on X and Y on M & X are logistic regressions. Thanks in advance, Bill 


You can use MODEL INDIRECT to obtain the indirect effects. In the input you showed earlier, you will obtain probit regressions with the default weighted least squares estimator for categorical dependent variables and linear regressions for continuous dependent variables. The indirect effect is the product of the two regression coefficients. You will obtain standard errors using the Delta method and can also request bootstrap standard errors. 


Linda I am still not hitting the mark. I ran the Syntax below, to estimate the indirect effects. But as can be seen from the output below, the estimate for the effect from X to Y via M is 0. The data input to this analysis was generated randomly, and was designed to have a net indirect effect. I do not know if this is related, but the model Indirect statement is the only keyword with the colon that does not change to blue in the syntax file. All others like data:, variable:, Model:, etc change color as soon as the colon is applied. Once again, Thanks in advance Bill CODE: title: Mediation Dichotomous data: file= 'C:\test.txt'; variable: names=X M Y; USEVARIABLES ARE X M Y; CATEGORICAL ARE Y; MODEL: Y ON X; Y ON M X; MODEL INDIRECT: Y VIA M X; Output: MODEL RESULTS Estimates S.E. Est./S.E. Y ON X 0.391 0.084 4.675 M 0.382 0.041 9.393 RSQUARE Observed Residual Variable Variance RSquare Y 1.000 0.198 TOTAL, TOTAL INDIRECT, SPECIFIC INDIRECT, AND DIRECT EFFECTS Estimates S.E. Est./S.E. Effects from X to Y via M Sum of indirect 0.000 0.000 999.000 


You would need to send your input, data, output, and license number to support@statmodel.com so I can see what is happening. I suspect you are not using Version 4.1 and that you are running into a bug from an earlier version. 


Dear Dr. Muthén, I have a question concerning the standardized output in a mediator analysis, in which "X" is a binary (manifest) predictor (gender), "M" is a continuous latent (factor) mediator (based on categorical items), and "Y" is a continuous latent factor outcome variable (based on categorical items). The problem is that I do not receive any error message, but the standardized outputs for SE, pvalues, and indirect effects are not printed (in contrast to the unstandardized output). As the standardized outputs usually have to be reported in papers, I want to ask if you know a solution. Alternatively, if the standardized estimates are not estimated in MPlus by default, what would you suggest to report? Syntax: names=X M Y; USEVARIABLES ARE X M Y; Categorical ARE "indicators of M and Y" ANALYSIS: TYPE IS GENERAL; ESTIMATOR IS WLSMV; MODEL: M ON X; Y ON M X; MODEL INDIRECT: Y IND M X; Thank you very much! 


With WLSMV, we don't give standard errors and pvalues for standardized estimates when the model contains covariates. 


Thank you very much for the quick reply! A reviewer asked us to provide standardized estimates. Do you suggest to report unstandardized estimates to show significant influences of mediators and to explain that Mplus does not report standardized estimates of SE and pvalues when using WLSMV and covariates? Do you have any other suggestions for alternative procedures or a reference we could cite? 


Yes. No. 

Chie Kotake posted on Tuesday, June 24, 2014  12:32 pm



Hi! I have: a) binary observed moderator B) latent predictor(4 continuous indicators) c) continuous observed outcome. My model is a multigroup model testing these relations: a>c B>c B*a>c (I created the interaction using XWITH). When I ran this model, I got this message: THE STANDARD ERRORS OF THE MODEL PARAMETER ESTIMATES MAY NOT BE TRUSTWORTHY FOR SOME PARAMETERS DUE TO A NONPOSITIVE DEFINITE FIRSTORDER DERIVATIVE PRODUCT MATRIX. THIS MAY BE DUE TO THE STARTING VALUES BUT MAY ALSO BE AN INDICATION OF MODEL NONIDENTIFICATION. THE CONDITION NUMBER IS 0.884D15. PROBLEM INVOLVING PARAMETER 23. THE MODEL ESTIMATION TERMINATED NORMALLY It seems this message appear when one of the variables used in the interaction term is binary since this did not happen when I used a continuous moderator. Is my understanding correct? If not, what could be contributing to this message? Thank you so much for your assistance! 


Please send the output and your license number to support@statmodel.com. 

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