Using the grm function (graded response IRT model) in the ltm package I
receive the following error:
Error: subscript out of bounds
for several scales I'd like to examine. Here's a small example that if
run a
few times will likley produce the error at least once
ch<-array(round(runif(50,1,5)),c(10,5))
grm(ch,start.val="random")
## or
grm(ch,constrained=F,IRT.param=T,start.val="random")
I have cannot figure out where I have gone wrong and was unable to find
mention of similar errors in the archives. Any help would be much
appreciated. A subset of my actual data that produces the same error is
pasted below
Thank you,
ben
t2_sr1 t2_sr2 t2_sr3 t2_sr4 t2_sr5
1 5 1 5 5
1 4 1 4 4
4 2 4 2 1
4 5 4 1 4
1 5 5 1 5
1 4 1 5 5
3 2 4 2 4
5 3 5 1 1
4 2 4 4 2
1 4 1 4 5
2 4 4 4 2
1 4 2 3 4
2 2 4 3 2
2 4 2 3 3
4 3 2 3 3
2 5 2 5 5
1 4 1 4 4
3 3 2 3 4
2 4 2 3 4
3 3 3 2 2
> sessionInfo()
R version 2.9.2 (2009-08-24)
i386-pc-mingw32
locale:
LC_COLLATE=English_United States.1252;LC_CTYPE=English_United
States.1252;LC_MONETARY=English_United
States.1252;LC_NUMERIC=C;LC_TIME=English_United States.1252
attached base packages:
[1] splines stats graphics grDevices utils datasets methods
base
other attached packages:
[1] car_1.2-16 epicalc_2.9.2.7 survival_2.35-4 foreign_0.8-37
faraway_1.0.4
[6] ltm_0.9-1 polycor_0.7-7 sfsmisc_1.0-8 mvtnorm_0.9-7
msm_0.9.3
[11] MASS_7.2-48
loaded via a namespace (and not attached):
[1] tools_2.9.2
[[alternative HTML version deleted]]
Ben,
This is because you do not have all the possible response options
represented for each item. For example, in your data below, item 2 has
no '1's.
I don't know if there is a workaround for this (other than deleting an
item or faking a response), or if this is a function of IRT itself?
Tom Fletcher
-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of ben kelcey
Sent: Wednesday, October 14, 2009 4:32 PM
To: r-help at r-project.org
Subject: [R] ltm package error for grm (IRT)
Using the grm function (graded response IRT model) in the ltm package I
receive the following error:
Error: subscript out of bounds
for several scales I'd like to examine. Here's a small example that if
run a few times will likley produce the error at least once
ch<-array(round(runif(50,1,5)),c(10,5))
grm(ch,start.val="random")
## or
grm(ch,constrained=F,IRT.param=T,start.val="random")
I have cannot figure out where I have gone wrong and was unable to find
mention of similar errors in the archives. Any help would be much
appreciated. A subset of my actual data that produces the same error is
pasted below
Thank you,
ben
t2_sr1 t2_sr2 t2_sr3 t2_sr4 t2_sr5
1 5 1 5 5
1 4 1 4 4
4 2 4 2 1
4 5 4 1 4
1 5 5 1 5
1 4 1 5 5
3 2 4 2 4
5 3 5 1 1
4 2 4 4 2
1 4 1 4 5
2 4 4 4 2
1 4 2 3 4
2 2 4 3 2
2 4 2 3 3
4 3 2 3 3
2 5 2 5 5
1 4 1 4 4
3 3 2 3 4
2 4 2 3 4
3 3 3 2 2
> sessionInfo()
R version 2.9.2 (2009-08-24)
i386-pc-mingw32
locale:
LC_COLLATE=English_United States.1252;LC_CTYPE=English_United
States.1252;LC_MONETARY=English_United
States.1252;LC_NUMERIC=C;LC_TIME=English_United States.1252 attached
base packages:
[1] splines stats graphics grDevices utils datasets methods
base
other attached packages:
[1] car_1.2-16 epicalc_2.9.2.7 survival_2.35-4 foreign_0.8-37
faraway_1.0.4
[6] ltm_0.9-1 polycor_0.7-7 sfsmisc_1.0-8 mvtnorm_0.9-7
msm_0.9.3
[11] MASS_7.2-48
loaded via a namespace (and not attached):
[1] tools_2.9.2
[[alternative HTML version deleted]]
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