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Mplus Discussion > Categorical Data Modeling >
 Arjan Berkeljon posted on Wednesday, February 18, 2009 - 6:32 pm

In trying to fit a polytomous (3-category) IRT model using Mplus (5.1) I have run into the following. To recover the IRT parameters I want to write a script to parse Mplus output. Using the syntax "SAVEDATA: ESTIMATES ARE "estimates.dat";" I am able to write the correct estimates to a file. What I do not get is how the numbers in this file map onto the numbers in the Mplus 'Model results' output.

The SAVEDATA command gives the following:

0.000 0.000 0.000 0.000 0.000 1.730 1.730 1.730 1.730 1.730
1.000 0.000 1.000 0.000 0.000 1.000 0.000 0.000 0.000 1.000
0.000 0.000 0.000 0.000 1.000 0.000 0.000 1.000 1.473 3.456
-1.433 0.978 -0.862 1.105 -0.833 1.490 -1.072 0.280

I assume elements 5-10 of the output are the loadings and that the last 10 elements are the thresholds. However, I cannot deduce what the other values are (i.e. the first 5 elements of 0 and the 0s and 1s in elements 11-28) and could not find anything online or in the manual. Any help would be greatly appreciated.

Thank you,
 Linda K. Muthen posted on Wednesday, February 18, 2009 - 6:47 pm
The file created using the ESTIMATES option is meant for use in a Monte Carlo study. You should use the RESULTS option. It will be shown in the output what is saved and the format. The parameter estimates and standard errors are saved according to the order of the parameters in TECH1.
 Arjan Berkeljon posted on Wednesday, February 18, 2009 - 9:31 pm
Understood. Thank you.
 Kelly Lundstrom posted on Wednesday, April 18, 2012 - 6:19 pm

I am wanting to save the (26x26) tetrachoric covariance matrix from EFA. I am using the following commands:


While I can get the lower-triangular covariance matrix by this process, it is saved in a manner that does not look like the output from Mplus. (It is saved as 5 columns, 70 or so rows, plus one element on the last row.)

Is there a way to change the format for how this matrix is saved? Ideally, I would like it in matrix format (26 by 26) in a txt document, so that I can then import this matrix into another statistical program. But, I'm open to other options that would make the matrix easier to import into other programs as well.

Any suggestions would be appreciated!

 Linda K. Muthen posted on Thursday, April 19, 2012 - 10:09 am
There is no way to change the format of the saved data.
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