[Rasch] multiple occasions

Petroski, Greg PetroskiG at health.missouri.edu
Tue Feb 9 09:02:08 EST 2010

I am still wrestling with the problem of scoring a single instrument administered on multiple measurement occasions to the same individuals.  It seems there are three options.

1.  The "stacked approach" in which data from K occasions from N individuals is stacked and items are calibrated and "ability" estimated as though there are NxK individuals.  This is easy to do and it would seem like the item parameters are then the average parameter values over all occasions.  So it is an appealing idea & easy to do.

2.  Estimate item parameters from the first occasion then estimate ability for all occasions as though the items were known.  Does this sound plausible?

3.  Separate calibrations, followed by an equating step.  This is technically the least pleasant option, but does it have some merit that I am missing?

Greg Petroski

U. of Missouri

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