Respecting priorities versus respecting preferences in school choice: When is there a trade-off ?

A classic trade-off that school districts face when deciding which matching algorithm to use is that it is not possible to always respect both priorities and preferences. The student-proposing deferred acceptance algorithm (DA) respects priorities but can lead to inefficient allocations. The top trading cycle algorithm (TTC) respects preferences but may violate priorities. We identify a new condition on school choice markets under which DA is efficient and there is a unique allocation that respects priorities. Our condition generalizes earlier conditions by placing restrictions on how preferences and priorities relate to one another only on the parts that are relevant for the assignment. We discuss how our condition sheds light on existing empirical findings. We show through simulations that our condition significantly expands the range of known environments for which DA is efficient.
info:eu-repo/semantics/published