[Rasch] assessing construct validity over time

Alexander Freund pafreund at uni-muenster.de
Wed Jul 25 01:43:59 EST 2007


I have a question I hope I can get a helpful answer to.
I'm investigating retest effects for an intelligence test (dichotomous 
scoring) over 4 test administrations. I would also like to check if the 
construct measured with my items changes over time. At every time point, 
I have sets of 15 items, and I'm using the same 15 items at points 1 and 
3, and a set of item isomorphs at points 2 and 4. So essentially, every 
subject delivers 60 answers, and 2 answers each for 30 items, 
respectively. My question is how can I use Rasch methodology to assess 
the construct validity of these items over the 4 time points? Is it 
legitimate to simply try to fit one Rasch model to all 60 items? Or what 
can be done in this case? I would be very thankful for any advice.

Best regards,

Dipl.-Psych. A. Freund
Psychologisches Institut IV
Fliednerstraße 21
D-48149 Münster
+ 49 251 83 34153
pafreund at uni-muenster.de

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