It would be crazy if Duke was able to fill their class with only admits and the minuscule acceptances from the wait list thus far.
I don't know exactly what admissions does to determine how many people to extend admits to in each round but my assumption is that they target a certain percentage of the class to fill in each round, with leeway to accept more or less depending upon what kind of applications they receive. I think their principle risk is admitting too many people and being unable to accommodate all of them, in which case they would make unrealistic assumptions to mitigate (like assume an 80% yield, double their historical rate).
Running with this, for a class of about 450 they would offer admission to roughly 560 people in total. If the rumored 60% yield is accurate that means ~340 accept, which leaves 110 spots. Obviously the assumptions that I am making aren't the same that the adcom made since 110 open spots would have the waitlist flying.
The point I am trying to make is that if they are full already then they must have made a yield assumption that was pretty close to on the nose. Perhaps a 50% increase in yield yoy qualifies as an "unrealistic" assumption as I outlined earlier. Unfortunately for us watlisters that means that they may have guessed their actual yield
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I'm getting pretty ancy in any case.