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Sarah Bragg posted on Friday, January 09, 2015 - 1:13 pm
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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 |
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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. |
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fulya baris posted on Wednesday, February 01, 2017 - 1:10 am
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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 ? |
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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. |
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fulya baris posted on Wednesday, February 01, 2017 - 11:15 pm
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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. |
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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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