[Rasch] Facets feature or bug?

Iasonas Lamprianou liasonas at cytanet.com.cy
Mon Apr 2 16:53:06 EST 2012


Dear all,
I send this question to all, and not only to Mike, because this question is both related to the Facets software, but is a methodological question as well.

I am running a "typical" scenario where I have markers who mark the responses of students to a test. The markers do not see the whole test, but only individual questions. We do NOT have double marking. So, lets say that we have 1000 students, each one responding to 10 questions. In effect, we have 10.000 responses. Lets say that each one of the 10.000 responses is randomly sent once to one marker. We have 20 markers in total.

Observation 1: the 3-d matrix markersXitemsXstudents is VERY sparse (we will all agree on that) because we have NO double marking
Observation 2 which is a question as well: I think that the design is NOT linked (no double marking), does everyone agree? However, Facets does not complain about disconnected subsets, I do not know why. Should I not worry? Does Facets assume that because of randomness, all markers are on the same scale? Is Facets confused and incorrectly thinks that the design is NOT disconnected?

Question: If disconnected subsets is a problem in this case, how can I run an anlysis in order to identify marker effects using this dataset?

Thank you for your help

Jason



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