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To give some context: I'm quite new to quantitative research in social sciences and learned about IRT, Rasch Reliability and Wright-Maps yesterday.

Today a colleague sent me this image:

enter image description here

and asked how it could be, that a single item can have multiple difficulities associated with it (see the marked coordinates).

As i understand it the Wright-Map was constructed by first gathering the cognitive abilities of the students and then letting them go through a test. The difficulties (coordinates on the right hand side of the diagram) were constructed by correlating the test-results with the cognitive-abilities of the corresponding student using a Rasch-Reliability-test.

I couldn't find anything related on the internet and since i'm quite new to the field myself don't already have a full overview of resources i could utilize.

Can someone elaborate?

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  • $\begingroup$ are those polytomous items? $\endgroup$ – Tom Mar 16 at 3:33
  • $\begingroup$ Yes, that is the case $\endgroup$ – Tim Hilt Mar 16 at 8:37
  • $\begingroup$ then those should be category-wise difficulties $\endgroup$ – Tom Mar 16 at 8:59

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