generally, most schools interview between 10-20% of the applicant pool and offer spots to a third of those interviewed. this is the case at columbia and upenn. while others like tufts university interviews about the same amount but offers 80% of those interviewed a spot in the upcoming class. when you get invited to interviews, almost all schools will be upfront with those stats, so feel free to ask. also, you should be able to find these stats in the school of interest's website. good luck.