A few years back, the NRMP published a short document called the Impact of Length of Rank Order List on Main Residency Match Outcome:2002-2016. There, the NRMP reported that matched applicants consistently had longer rank order lists than unmatched applicants.
This data is a bit old, but it assesses over a decade of Matches, so I take it seriously. In my mind, what it means to those approaching the residency application process is that candidates should throw a wide net in choosing programs at which to apply. Of course, there is a financial cost to this strategy, and that expense needs to be balanced. However, according to this data, starting out with more options usually will provide more opportunities to interview and thus, the ability to create a longer rank order list.
