Ever since Harvard announced it would accept more than 150 waitlisted high school seniors, the effects have been felt in many top-tier schools, including Northwestern.

The ripple effect has delayed the admission process here, as students accepted to Northwestern could decide to leave for schools where they had been waitlisted, Associate Provost Michael Mills said Wednesday.

Although high school seniors were supposed to choose a college by May 1, and Northwestern usually has a rough assessment of its incoming freshmen by now, the class of 2012 is far from finalized.

“This year’s different,” Mills said, “because all of our peers, with the exception of Stanford, are pulling heavily from their waitlist. That has downstream consequences for everybody, including Northwestern.

“When we’re actually going to have confidence in our numbers, I don’t know,” he added. “We’re not there yet, but in a couple of weeks, maybe.”

For Mills, many factors affected this year’s admissions season.

“I think kids apply to more schools to begin with than they did five or ten years ago,” he said. “Some of it has to do with the Common App.”

He added that “as it gets more difficult to get into elite schools, you’re going to have to hedge your bets.”

Mills said that high school seniors who apply to top universities tend to apply to the same ones, such as Yale, Harvard, University of Chicago and Northwestern.

“That phenomenon causes everybody’s predictions to be out of whack,” Mills said.

But Mills said he wasn’t worried that the downstream effect would cause a drop in the quality of Northwestern’s freshmen class.

“We’ll get our class, it’s just a matter of who it’s going to be,” he said. “We’re going to reach our target, it’s going to be a very strong freshman class.”