[Rasch] Interpretation of Item Plot

Petroski, Greg PetroskiG at health.missouri.edu
Sat Mar 24 15:09:44 EST 2007

To keep the size of this e-mail small I put an item plot on PhotoBucket.


The item is ordinal with responses 0 to 4 with larger values indicating greater ability.  Note that two of the five catagories do not ever have the highest probability of being endorsed.  Am I correct in interpreting this as suggesting a defective item -- one that might work as well with only three categories?

Greg Petrsoki
U. of Missouri - Columbia 

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