My data is 2688 by 200, with 0/1 coded. I am trying to estimate both parameters and ability(theta) using 2PL logistic model.
First I use the following code to get parameter estimate:
fit2PL = ltm(dat ~ z1, IRT.param = TRUE)
Then use the following to get theta estimate
Now I want to extract zl column (i.e., theta estimate) from theta, the following code is not working. please help