Hello, I created an IRT model (generalized partial credit model) based on 2 different groups (male/female). The items are 7-point Likert-type. My command was:

The model runs fine and I get results that make sense. When I then run

All parameters (thetas) other than the mean and variance are identical (see numbers for only var3 and overall mean / variance). How can it be that everything is identical but then mean / variance are different?

And finally (and most importantly), I would like to generate category response functions, boundary characteristic curves etc. However, when I then run:

Stata says: "Nothing to draw."

What am I doing wrong?

Thanks!

..................male ................female

Discrim 5.8792584 ........5.8792584

Diff

2 vs 1 -1.7224575..........-1.7224575

3 vs 2 -1.0862329 ..........-1.0862329

4 vs 3 -.72656654 ..........-.72656654

5 vs 4 -.30533028.......... -.30533028

6 vs 5 .06475272 .............06475272

7 vs 6 1.0806044 ............1.0806044

mean(Theta) 1.110e-16 ......-.46675985

var(Theta) 1 ....................1.4448088

**irt gpcm var1 var2 var3, group(sex)**The model runs fine and I get results that make sense. When I then run

**estat greport**All parameters (thetas) other than the mean and variance are identical (see numbers for only var3 and overall mean / variance). How can it be that everything is identical but then mean / variance are different?

And finally (and most importantly), I would like to generate category response functions, boundary characteristic curves etc. However, when I then run:

**irtgraph icc var1 var2 var3, group(sex)**Stata says: "Nothing to draw."

What am I doing wrong?

Thanks!

..................male ................female

Discrim 5.8792584 ........5.8792584

Diff

2 vs 1 -1.7224575..........-1.7224575

3 vs 2 -1.0862329 ..........-1.0862329

4 vs 3 -.72656654 ..........-.72656654

5 vs 4 -.30533028.......... -.30533028

6 vs 5 .06475272 .............06475272

7 vs 6 1.0806044 ............1.0806044

mean(Theta) 1.110e-16 ......-.46675985

var(Theta) 1 ....................1.4448088

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