Anton's numbers have to be at least a little bit wrong. The waitlist email said that no more than 100 applicants are waitlisted. (Still an absurd number for a school that never admits more than 20 off of that list. But forget about that.) LSN seems to be showing about 25 people as already on that list. If you assume -- conservatively -- that that sample represents about 1/3 of the total group, then, even if Anton is right that there are only 16 slots left, that still leaves the purgatory group at around 40. Personally, I would guess that it's between 20 and 30, which may not be horrible odds.

I just tried to post something like this, but I ran through more numbers. If they've waitlisted 75 people already and are filling all 100 waitlist slots and everyone on the purgatory list who's not accepted joins the waitlist and they offer exactly as many purgatory list acceptances as they have slots and they have 16 slots, that gives us a 16/41 = 39% chance of acceptance.

Reasons it could be better than that:

(1) They might have waitlisted more than 75 people.

(2) They might plan to waitlist fewer than 100 people.

(3) They might have more than 16 slots.

(4) They might offer more purgatory acceptances than they have slots. If they make offers assuming the 80% yield, the expected number of people in the purgatory group goes up to 46 and the probability goes up to 44.4%

Reasons it might be worse:

(1) If historically most people waitlisted off the purgatory group decline to enter the waitlist, the purgatory group would be larger. (because my calculation for purgatory group is acceptances + waitlist offers. if they plan to offer more than 25 waitlist offers because not everyone who gets a waitlist offer will take it, the expected size of the purgatory group goes up).

(2) They might have fewer than 16 acceptances to offer.

(3) They're trying to fill de facto quotas and the "queer disabled middle-class white male humanities major" slot is taken.