[R] Ability Estimates for Repeated Measurements in the eRm Package

Tessari tessari at umich.edu
Wed Sep 2 17:49:48 CEST 2009


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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