1. Mplus availability
2. Saving Mplus command files on the Windows Terminal Server
3. Mplus Defaults

Mplus Availability

Question:

I would like to use Mplus to perform a path analysis, a confirmatory factor analysis, or a structural equation model. How can I access this software at UT?

Answer:

Click HERE for up to date information on how to access Mplus at UT.

If your models of interest are small, the free demo version may be sufficient to meet your needs.  Download the free demo version of Mplus from the Muthén & Muthén Web site for your own personal computer.

Saving Mplus command files on the Windows Terminal Server

Question:

I am using Mplus on the ITS Windows Terminal Server (WTS). When I open an Mplus command file and run it, it works fine. When I use Save As in the File menu to save the command file under a different file name, Mplus doesn't work. What is wrong?

Answer:

Mplus was not specifically written for the Windows terminal server environment, so several oddities can arise when you use it in this environment. One unusual feature is that if you save a previously working Mplus command file, you must exit Mplus and relaunch it. Then your saved file should work correctly. Note that you can modify an existing command file within Mplus without exiting the program.

Also, you should be sure to save each command file before you run it through Mplus' command interpreter (i.e., save your command file before you run your model). Mplus writes its output information to the user's window by default; if you want to reaccess your original command file you must open it again by using the File menu and selecting the Open option or the list of the four most recently-accessed files located at the bottom of the File menu.

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Mplus Defaults

Question:

What are the defaults for the Mplus program?

Answer:

According to the Mplus User's Guide, page 23:

If a parameter is not free by default, once a parameter is mentioned using the MODEL command, it is freed at the default starting value unless another starting value is specified using the * option or the parameter is fixed using the @ option. The exception to this is that the variances and residual variances for latent response variables corresponding to categorical dependent variables may not be free.

Following are the default starting values of other parameters:

Default settings are used to simplify the model specification. In order to minimize the information provided by the user, certain assumptions are made about the means/intercepts/thresholds, the variances/residual variances, and the covariances in the model. These assumptions are based on what is most commonly seen in practice. The user can override all defaults. It is important to understand the default settings so that the estimated model is the model that the user expects.

• Following are the default settings for means/intercepts/thresholds in the model when they are included:
• Means of observed independent variables are estimated as the sample values.
• Intercepts and thresholds of observed dependent variables are free.
• In single group analysis, means and intercepts of continuous latent variables are fixed to zero.
• In multiple group analysis, means and intercepts of continuous latent variables are fixed to zero in the first group and are free to be estimated in other groups.
• Means and intercepts (probabilities) of the categorical latent variable are free.

Following are the default settings for variances/residual variances:

• Variances of continuous observed independent variables are estimated as the sample values.
• Variances of continuous latent independent variables are free.
• Residual variances of continuous observed dependent variables and continuous latent dependent variables are free.
• Variances and residual variances of latent response variables for categorical variables are fixed to one.

• Covariances among observed independent variables are estimated as the sample values.
• Covariances among continuous latent independent variables are free.
• Residual covariances among observed dependent variables and of continuous latent variables are fixed to zero with the following exceptions:
• Residual covariances of observed dependent variables are free when neither variable influences any other variable.
• Residual covariances of continuous latent dependent variables that are not indicators of a second-order factor are free when neither variable influences any other variable except its own indicators.

Reference

Muthen, L.K. and Muthen, B.O. (1998). Mplus User's Guide. Los Angeles: Muthen & Muthen.

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