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Message/Author
 Sarah Bragg posted on Friday, January 09, 2015 - 1:13 pm
Good afternoon,

I was trying to run a bifactor model in Mplus, but I have run into an error and did not know if you would have any suggestions.

Below is my input syntax:
ANALYSIS:
type = general;
ESTIMATOR = ML;
MODEL:
General BY
ITEM1*
ITEM3
ITEM4
ITEM7
ITEM9
ITEM10;
Optimism BY
ITEM1*
ITEM4
ITEM10;
Pessimism BY
ITEM3*
ITEM7
ITEM9;
General@1;
Optimism@1;
Pessimism@1;

General WITH Optimism@0;
General WITH Pessimism@0;
Optimism WITH Pessimism@0;

Output:
STDYX;

The system generates the following error:

THE STANDARD ERRORS OF THE MODEL PARAMETER ESTIMATES COULD NOT BE
COMPUTED. THE MODEL MAY NOT BE IDENTIFIED. CHECK YOUR MODEL.
PROBLEM INVOLVING THE FOLLOWING PARAMETER:
Parameter 24, ITEM10

To fix the problem, I tried setting Item10@0 in the syntax under the MODEL heading. When I do that, the model works perfectly. However, is there a better way to fix this problem, without assuming 0 error on Item 10?

Thank you very much for your time.

Sincerely,
Sarah Bragg
 Bengt O. Muthen posted on Friday, January 09, 2015 - 4:22 pm
The model looks correctly set up. Perhaps a large negative residual variance occurs. We would need to know more to diagnose this. Please send data, input, output, and license number to Support@statmodel.com.
 fulya baris posted on Wednesday, February 01, 2017 - 1:10 am
Hi Dr Muthen
I want to estimate person(theta) and item parameters( a, d) for bifactor model
Does mplusAutomation can do it ?
I coulndt find anything about it
would u help me pls ?
 Bengt O. Muthen posted on Wednesday, February 01, 2017 - 4:18 pm
Yes. Just specify a bi-factor model using the regular BY approach. And ask for factor scores (see UG) - they give you the estimated theta.

Mplus also offers exploratory bifactor analysis - see UG examples.
 fulya baris posted on Wednesday, February 01, 2017 - 11:15 pm
Thanx for your answer Dr. Muthen
I examined your Mplus examples about bifactor
I saw model results.. thera are factor scores u mean that they are person parameter( theta)
but I still couldn't find discrimination (a) and difficulty (a) parameters in your examples.
 Bengt O. Muthen posted on Thursday, February 02, 2017 - 5:41 pm
Bi-factor modeling lets every item be influenced by 2 factors. This usually is not described in terms of discrimination and difficulty parameters. See the FAQ on our website:

IRT parameterization using Mplus thresholds
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