General SEM Discussions

Hello!
Just a quick question: is it possible to do a multi level analysis with OpenMx?

Best wishes!

Nick

Hi,

in a structural equation model in RAM notation, one can easily write out the log-likelihood, as done by Bollen (p.107). My question: is the log-likelihood concave? In other words, do I need to worry about finding only local minima when mxRun tells me that my model converged? I'd be happy about any background reading on this.

Thanks and regards, Chris

I think this can be done, but I'm having problems seeing a clean solution. Is there a way with OpenMx to predict an outcome using the interaction of two latent variables?

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 ?

Hi

I'm totally new to OpenMx so please excuse me if I'm not posting at the right place or asking a stupid question:-(

I just got thourgh the nice User Guide but could not find examples on how to build a SEM model:-( Is it in the user guide under another name? My model would be:
Measurement model:
5 indic to latent exo C.Bez (with var to 1)
3 indic to latent exo C.HE (with var to 1)
1 observed endogenous variable C.Satis (with var to 1)

Structural model:
C.Bez and C.HE explain C.Satis

Question about handling covariates in SEM: Say you suspect sex should be controlled in a twin design. How do these three models differ in what they are testing?
1. An ACE model with raw data and sex in the means model (m+(b*data.sex)
2. An ACE model with raw data residualized for sex.
3. An ACE model allowing for sex-limitation but no covariate.

The omxGraphviz() function in OpenMx currently draws arrows by inspecting the A and S matrices and looking for values that are non-zero. Is that the correct criteria, or should it be (value != 0 || free == TRUE)? On a related note, what is the correct criteria for drawing arrows from the M matrix? Is it (value != 0) or (value != 0 || free == TRUE)?

hi all,
Summary provides Std.Errors for the free cells of matrices specified in the top model.

Questions:
Is there any way to get SEs for Algebras?

Given that SEs are not obtainable currently for Algebraic matrices - how should Std.Errors - in particular the 95%CIs of a matrix - be calculated when standardizing a solution?

Do the CIs of values in a the standardized matrix retain properties as the unstandardized? For instance, that a given CI doesn't include 0?

This forum item has a $5,000 answer (and a zero dollar answer).

http://psych.colorado.edu/~carey/Bouchard/BouchardPrize.php

Greg Carey is offering an economic stimulus package of $5000 cash to "the first person to demonstrate that C and E in the ACE model can act as legitimate variables in a causal model without the assumption that a specific, concrete environmental variable must correlate either 0 or 1 in siblings."