Hi,

I am pretty new to Stata and IRT. Using IRT 2PL model, I tried to estimate item difficulty and item discrimination parameters. There are 17 items (binary: 1-yes, 0-no) and the sample size is only 31.. I admit the sample size is too small, but anyway I analyzed it and most of item discrimination parameters were negative values. Can anyone explain the negative discrimination? Does it simply mean that I cannot trust the results from a small sample size or that item coding is wrong, etc? Plus, how can I check df for each item?
Thank you in advance!