This data is the relation of contiguous rank list length to success in matching. Contiguous rank list length is the number of GS programs in a row on your list. "Success" is defined as matching into any GS program. So if you matched to IM after ranking 5 GS and 5 IM programs alternating 1 GS and 1 IM, you would have a CRLL of 1 and would count as not-matching. If you only ranked 4 programs, all GS, and didn't match your CRLL would be 4 and you would count as not matching.
US Senior Unmatched Rate in GenSurg by Contiguous Rank List Length
1-2 62%
3-4 41%
5-6 44%
7-8 18%
9-10 13%
11-12 6%
13-14 4%
15+ 5%
Take home message here seems to be that adding programs to your rank list is very valuable up until 11-12 after which you abruptly hit diminishing returns.