From: sanchez ana <paolas25mx_at_yahoo.com.mx>

Date: Fri, 04 Jun 2010 12:30:43 -0700 (PDT)

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Since the model has constructs that are measured with only one item, I decided to connect directly the variable (item) to the other constructs.

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Fri 04 Jun 2010 - 19:33:15 GMT

Date: Fri, 04 Jun 2010 12:30:43 -0700 (PDT)

Can somebody help me with the following issue (SEM in R), please:

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When I run the model (includes second order models) in R, it gives me the following:

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1) In sem.default(ram = ram, S = S, N = N, param.names = pars, var.names = vars, :

Could not compute QR decomposition of Hessian.

Optimization probably did not converge.

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2) I have aliased parameters and NaNS

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or sometimes when I run it again I have the following message:

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1) Error in solve.default(C) :

The system is computationally singular: condition number = 4.28182e-19 (it says so in Spanish)

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Since the items are measured in likert scales I was using polychoric correlations, however, I saw that it can cause troubles, so I decided not to use it anymore. I also check the following:

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1) Variables with variance 0 (I do not have) 2) Linear combinations of variables (I do not have high correlations) 3) I already used initial values for the aliased parameters 4) I do not have missing data 5) The eigenvalues of the S matrix are all positive (no zeros) 6) I calculate the determinant of the correlation matrix, adding one variable at a time, in order to look for multivariate dependencies, but the determinants are not cero, the lowest one is:0.0004054475

Since the model has constructs that are measured with only one item, I decided to connect directly the variable (item) to the other constructs.

Thanks

Ana

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https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Fri 04 Jun 2010 - 19:33:15 GMT

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