Bifactor model visualization

[Farah Isse Mumin]

Dear Phil and team,

The bifactor model provides the best fit for my data, as it captures both a general construct and specific subfactors. The model fit is quite strong, but I’d like to take it a step further by generating ICCs, IIFs, and TIFs. I haven't been able to do this using the mirt package, or I might be missing something. Any guidance would be greatly appreciated.

thanks

[Jay Verkuilen]

I've been using a bifactor model recently and was working on doing the same thing. Part of the issue is that a bifactor model is inherently multidimensional, so it's necessary to cope with that. Plot will usually just show you two dimensions in a contour plot, which is likely not so useful. You'll have to work with extract.item and then the iteminfo function to compute information. This is a pretty complicated function with a lot of options so plan for experimentation. With a MIRT model you'll need to either think of a direction in the coordinate space set up by the model to get a single function or form an information matrix. The multidimensional example in iteminfo is only for a 2D exploratory model so if Phil (or anyone else) has a good example of how to get this for a bifactor model with, say, four bifactors, that would be great!

I think the example at the end of the help for iteminfo may be in error given that it has angles listed as 90,0; I think 90 is implying being orthogonal to the first axis, but maybe I'm mistaken and just don't understand what it's doing.