We need to score a combined test of English + Maths + Science. Would prefer to take IRT route to classical scoring as want to identify top 0.5% performers. Looked into multidimensional models as an possible solution.
The literature on MIRT talks about loading on multiple skills but could not find any actual use case similar to what I need to do.
Is there any theoretical/empirical guidance on how disparate the skills can be. Is MIRT only used for a subject and subskills within that or multiple subjects can be merged?