Mon, 03/15/2010 - 04:38

Hello,

I have a set of 4 correlated continuous variables that I have observed, and also a fifth binary observed variable that has an effect on 2 of the 4 continuous variables.

I want to test the hypothesis that a single latent factor plus the fifth binary observed variable are together sufficient to explain the covariance matrix for the 4 correlated continuous variables.

How can I test this in OpenMx ?

Also, what category does this fall under (so I can google for it or look it up in textbooks) ? Is there a place where I could read up on this (ideally with examples from OpenMx, or LISREL or AMOS) ?

Thanks much !!!!!!!!

Suresh

Take a look at the books under the Resources tab at the top of this page.

I'd recommend reading Maruyama (1998) Basics of Structural Equation Modeling or Marcoulides & Schumacker (1996) Advanced Structural Equation Modeling: Issues and Techniques. That should get you started with the ideas.

Another way to get started is by looking at my class notes at http://openmx.psyc.virginia.edu/forums/openmx-help/teaching-sem-using-op...

Thanks much for the links !!

I managed to figure out how to do the analysis (in R with the sem package, and in LISREL) with just the one latent factor. What I am struggling with is to figure out the right way to now include the binary observed variable as an explanatory factor in the path diagram..

I will read as well.

Very best, Suresh

The analysis is not all that difficult in OpenMx. I would take the script from the OpenMx homepage http://openmx.psyc.virginia.edu/ and add a definition variable for the binary explanatory variable. To do this, take a look at, e.g., http://openmx.psyc.virginia.edu/docs/OpenMx/latest/DefinitionMeans_Path.... and see if you can construct a model in which the binary variable has an effect on the mean of each of the observed variables.

Thank you, yes, that seems like what I am looking for.

I also finally need to figure out how to do some missing-data imputation (like FIML in LISREL); I saw some previous posts that advised that other R packages for imputation could be combined with OpenMx for this. I will try to follow those leads..

Very best, Suresh

Your reply is a little confusing; OpenMx has built-in FIML functions, and FIML does not require any imputation. It simply calculates the likelihood (on a case-by-case basis) of those variables that have been observed. I hope that this is clear from the examples, but please let us know if it is not.

A question like that came up at a talk recently, from an epidemiologist used to using regression: I think from that framework, people often think that FIML involves imputation, and ask "can I see what it looked like in the raw data?" not knowing that it was the raw data...

Yes, mea culpa ! I spoke to a genuine expert on factor analysis and in our brief discussion, he told me to use FIML to handle the missing data in LISREL, and I then mistakenly assumed that it uses some "reasonable" method to "fill in" the missing data.

I will go through the examples and other material now !

thank for the updates..