I think that the data was provided by AAMC at the time.... some people also suspected that some schools would call people on the waitlist and ask if someone would accept an offer if it was made and if the answer was "no" an offer would not be made. That way a school could decrease the number of offers made as the denominator over the numerator, offers accepted.
This seems to have evolved over time, and seems pretty widespread today insofar that a ton of schools encourage us to send expressions of interest, if not intent, if we are on the WL. Other than the tiny fraction of schools that still use ranked WLs,
I'd be shocked if schools didn't prioritize people who play the game over those who don't, and this can't help but goose their yields, at least a little. Several schools have already directly told me that they do take such expressions into account when deciding who to pull off their unranked WLs. And, I guess it makes sense for them to want to separate those who remain genuinely interested in the school from those who have mentally checked out after being disappointed over not receiving an initial A. I can confirm that I fall into both categories, depending on the school.
Schools like Mayo taking it to the next level by expecting LOIs before handing out initial As is probably the natural progression. Ethics and professionalism aside, however, expecting it earlier in the process kind of forces people into a corner where it's easier to justify lying. As has been said before, schools that do this deserve what they get.
Doing it in May to efficiently fill a class off the WL is one thing, and if a school chooses to allocate initial As and WL slots to maximize yield at the expense of potentially losing people who are disappointed they didn't receive an A up front, so be it. Doing it in January to pressure people to make a decision before they have visibility into what their options are, both with respect to As and to fin aid, is something else entirely. JMHO.
