[Rasch] Negative pt-bis and fit of 1.0? How can this be?

Stuart Luppescu slu at ccsr.uchicago.edu
Wed Mar 7 08:53:14 EST 2012


On Tue, 2012-03-06 at 15:36 -0600, Stuart Luppescu wrote:
> Are you saying that if I just generated 1's and 0's randomly and tried
> to calibrate them they would all fit? Hmmm. I'm going to have to try
> that.... 

Very interesting, indeed! Of course, you get 0 reliability and
point-biserials near 0, but all the fit statistics are very close to
1.0! Mark Moulton gets a beer next time I see him for providing the
instructional moment of the day.

-- 
Stuart Luppescu -=- slu .at. ccsr.uchicago.edu        
University of Chicago -=- CCSR 
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