I'm trying to use IRT to equate scales across 5 datasets. Three of them use the same scale (A); the other ones use different ones (B and C) There are items that overlap between A and C, A and B, but not B and C.
- Is it still possible to create commensurate measures across the three datasets?
- If I wanted to create a commensurate measure for A and B, I get that I need to use the anchor items...but what exactly is the role of non-anchor items? (that are unique to each dataset)? do they add any information?