[R] ability estimate with GRM of IRT
fshen at ufl.edu
Fri Jan 19 05:30:06 CET 2007
Hi my friends,
I have an issue with ability estimates when running GRM of IRT. I
have responses from 242 subjects but got 183 ability estimates.
Below is what I did to get the estimates.
1) I have a csv file "P1.csv" and I imported it into R and loaded
the "ltm" package by doing:
2) I created a subset that included columns 2 to 9 for the
analysis by doing:
3) I converted the subset into data.frame format by doing:
4) I checked the descriptive stats for the s1df by doing:
And it was confirmed that 242 subjects' responses were imported.
5)I ran GRM on the s1df dataset by doing:
6)Finally, I ran the ability estimated by doing:
And I got 183 factor-scores for observed response patterns.
Besides, the 183 estimates are not for the first 183 subjects of
the 242 because the response patterns of No 1 on the factor-scores
list do not match those of No 1 in the s1 dataset and the same
thing holds true for the rest of the response patterns.
Could you help me find out what the problem is?
Many thanks in advance!
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