Waitlists exist because it’s hard for schools to predict their yields. The yield is the percentage of accepted students that will ultimately enroll. If this number was known exactly, there would be no need for waitlists: schools would simply accept the exact number of students needed to fill the available slots.
But in practice, the yield can’t be predicted exactly. And schools have to be careful here. They don’t want to accept too many students, because if the yield is higher than expected, they will be overenrolled, which is a problem. It’s better to accept fewer students and to put a bunch on the waitlist. If the yield is lower than expected, that’s not a problem: they can just pull some additional students off the waitlist to avoid underenrollment.
Here are Lehigh’s waitlist numbers for the past 10 years, from their Common Data Sets:
Fall 2016: 66 waitlisted students admitted, out of 2127 accepting a place
Fall 2015: 0 of 1847
Fall 2014: 2 of 1296
Fall 2013: 39 of 1250
Fall 2012: 0 of 1337
Fall 2011: 1 of 1514
Fall 2010: 14 of 1206
Fall 2009: 43 of 1160
Fall 2008: 7 of 1388
Fall 2007: 72 of 1096
So the odds of getting in off the Lehigh waitlist have never been great during the past decade. There is little consistency from year to year, so last year’s results don’t really indicate very much.
You can see that Lehigh was in that category during 4 of the past 6 years.
Lehigh’s yields have generally been creeping upward in recent years, from 30.0% in 2007 to 35.7% in 2016. So it’s likely that Lehigh’s yields were higher than expected in some of those years. You don’t need to go to the waitlist in that situation; the waitlist is used when yields are lower than expected.