Howard,
You can estimate 3 parameter IRT models in gllamm
if the guessing parameters are treated as known.
It's a bit complicated to set up, but I could send
you a do-file.
If you need to estimate the guessing parameters,
you can use a profile likelihood method. However,
this is probably only feasible if all guessing
parameters are assumed to be equal.
Best wishes,
Sophia
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