[R] ability estimate with GRM of IRT

From: SHEN,FENG <fshen_at_ufl.edu>
Date: Fri 19 Jan 2007 - 04:30:06 GMT

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: p1<-read.table("P1.csv",header=TRUE,sep=",") library(ltm)
  2. I created a subset that included columns 2 to 9 for the analysis by doing: s1<-p1[,2:9]
  3. I converted the subset into data.frame format by doing: s1df=data.frame(s1)
  4. I checked the descriptive stats for the s1df by doing: ds1df=descript(s1df) ds1df

And it was confirmed that 242 subjects' responses were imported.

5)I ran GRM on the s1df dataset by doing: grm<-grm(s1df, Hessian=T)

6)Finally, I ran the ability estimated by doing: aes1=factor.scores(grm)

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!


R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Fri Jan 19 15:36:12 2007

Archive maintained by Robert King, hosted by the discipline of statistics at the University of Newcastle, Australia.
Archive generated by hypermail 2.1.8, at Fri 19 Jan 2007 - 08:30:26 GMT.

Mailing list information is available at https://stat.ethz.ch/mailman/listinfo/r-help. Please read the posting guide before posting to the list.