[R] Ability Estimates for Repeated Measurements in the eRm Package
Tessari
Dear R Users,
I am using the LLTM and the LRSM functions in the eRm package to do repeated
measurements where there are 2 measurement points for a list of 10 items. I
am trying to get ability estimates but am having trouble. I don't think
that it is appropriate to use the pmat function since the person parameters
are based on all 20 items. Rather, I think it would be more appropriate to
have the person parameters be based on the 10 items at Time 1 and then the
next 10 items at Time 2. However, I don't want to form 2 separate Rasch
models since I think it's important to have all 20 item parameters
calculated at once.
Any advice would be greatly appreciated. Also, if more information is
needed, I could send my sample code.
Best,
Kim
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and provide commented, minimal, self-contained, reproducible code.
Doran, Harold
the irt.ability() function in the MiscPscyho package for ability
estimates.
Tessari
Hello,
Thank you very much for the tip. I think that the irt.ability() function is
what I'm looking for but I'm not sure.
To be more clear, I have obtained item parameters from the LLTM function in
the eRm package which allows for repeated measurements. I have 10 items
measured at 2 time points, for a total of 20 item parameters. I wish to get
the ability estimate for a person at time 1 and then separately at time 2.
Here is the code I'm using but it doesn't seem to work.
ItemParams<-c(-0.199,-0.283,0.109 ,0.142 ,0.056
,-0.062,-0.125,0.066,0.153,0.142,
0.102,0.019,0.411,0.443,0.357,0.239,0.176,0.368,0.454,0.443)
Time1Params<-list("1pl" = list (b = ItemParams[1:10]))
Time2Params<-list("1pl" = list (b = ItemParams[10:20]))
irt.ability(c(1,0,1,1,1,1,0,1,1,1),Time1Params,method="MLE")
irt.ability(c(1,1,1,1,0,0,1,1,1,1),Time2Params,method="MLE")
Also, I've tried to locate the MP Vignette but have been unsuccessful.
Thanks again for your timely response. It's greatly appreciated!
Best,
Kim
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