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09-24-2014 08:39 PM

I am trying to estimate IRT a (item discrimination) and b (item difficulty) parameters from the probability of correct response (=p+ values) conditioned on each of the 8 theta points. Someone told me that I have to use logit function to get the "a" and "b" parameters. So I ran the proc Genmod procedure as shown below, but the result looks not right.

Data temp;

input theta p;

card;

-3.0 .001

-2.5 .015

---

2.5 .950

3.0 .998

;;;;

run;

proc genmod data=temp;

model p=theta / link=logit, dist=poi;

run;

Would you let me know what SAS function I have to use to get the correct "a" and "b" parameters?

Thanks!

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09-25-2014 03:41 AM

"The result looks not right?"

How it is not right?

Why do not you use PROC IRT?

or check this paper if it may help