Bifactor IRT models PreviousNext
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 Arjan Berkeljon posted on Tuesday, August 10, 2010 - 7:32 pm
I would like to fit a bifactor IRT model in Mplus. I have come up with the following syntax which, I believe, is a bifactor implementation of the Graded Response Model (Samejima, 1969; 1996):

** I simplified the syntax for posting
MODEL: G by i1-i4*; ! general factor
G@1; ! Variance at 1
[G@0]; ! Mean at 0
! specific factors
F1 BY i1-i2*;
F1@1; ! Variance at 1
[F1@0]; ! Mean at 0
F2 BY i3-i4*;
F2@1; ! Variance at 1
[F2@0]; ! Mean at 0
! uncorrelated factors
G with F1@0 F2@0;
F1 with F2@0;
! Item thresholds free
! First threshold
[i1$1];
[i2$1];
[i3$1];
[i4$1];
! Second threshold
[i1$2];
[i2$2];
[i3$2];
[i4$2];

Does this implementation seem sound or do I need to place additional constraints? Also, in a correctly specified bifactor IRT model, would recovery of IRT parameters be the same as in the single factor case (i.e. a standard IRT model specification)?

Thank you.
Sincerely,
Arjan Berkeljon
 Linda K. Muthen posted on Wednesday, August 11, 2010 - 10:16 am
The implementation looks correct. You should recover the parameters you need.
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