[Rasch] Polytomous data difficulty parameter

Mark Lavenia ml06e at fsu.edu
Sun Aug 31 11:36:40 EST 2008


I am working with data from a 5-category questionnaire. I'd like to present a table that indicates the rank order of subscale items by ease of endorseability. From what I have learned, polytomous data have difficulty parameters per threshold, but not an overall item-level difficulty parameter. I have heard from some that I should just a priori declare which threshold indicates endorsement, and use that difficulty parameter. I have heard from others that I should average all the threshold difficulties together to calculate an overall difficulty. First, is it correct that there is no such thing as an overall difficulty parameter for polytomous data (per item)? If no, how is it calculated. If yes, what is the best approach to deriving a statistic that could meet my purpose mentioned above? Gratefully yours, Mark



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