All schools–including Stanford and Harvard–play games to increase their yield and decrease their admit rates. Having said this, Stanford’s performance versus Harvard is even more impressive than it might at first appear because of three things:
First, Stanford probably admitted too many students this year. This obviously affected the admit rate and probably the yield rate. This year 1,722 freshmen matriculated; last year it was 1,691. Although there have been rumors of a policy to increase the undergraduate enrollment, little has been made official. More telling is that Stanford had to re-open some closed, off-campus housing because of a higher than expected yield. This suggests they over-accepted. Harvard, in contrast, admitted 93 students from its waiting list. This means it could fine tune the number of incoming students.
Second, Harvard admitted more students (both in absolute numbers and relative to the size of the eventual class) through the early round than Stanford did. Harvard admitted 977 early. This was 16.5% of those who applied early and about 59% of those who eventually enrolled. To be sure, in contrast to most schools, at both Harvard and Stanford the early admits are not required to enroll. Yet the evidence is that most do even at these two schools. (Having said that, I know two kids who were admitted early to Harvard and both ended up going to Stanford.) Stanford admitted 742 early. This was 10.1% of those who applied early and 43% of the admitted class (assuming all early admits attend, which they don’t but most do).
Third, Harvard admitted 93 kids off of the waiting list but Stanford apparently did not admit anyone from its waiting list. This is probably the biggest of the three factors. My guess is that virtually everyone who is offered a place off of the wait list at Harvard matriculates. I say so for a few reasons. First, you have to affirmatively accept a place on the wait list. If Harvard isn’t your first choice and you are in at your first choice, why go to the wait list? I’m sure a few kids play games, but my guess it is not a lot. Second, kids and (more importantly) their schools can signal to Harvard that if admitted they will attend. Don’t doubt that the admissions staff takes notice. They want as high a yield rate and as low an admit rate as possible. Finally, when taken off of the Harvard wait list, you get a phone call in addition to an email. To be sure, you have the right to decline the offer (and I assume it counts as an offer), but how often does this happen? My guess is that in a number of cases, at Harvard and beyond, an admissions person calls the counselor and says “will Mary accept if we offer her?” The high school counselor has an incentive to tell the truth because in all likelihood, someone else will be applying from his high school to Harvard next year. Once the college receives a favorable signal–but not until then–it admits the kid off of the wait list.