COE has nothing to do with it.

This is another study on pubmed from JAMA, comparing bariatric surgery procedures and their complication rates to get a handle on what made things go wrong, if they did. Total complication rate for all surgeries was 1.6 percent. Sleeve surgeries alone had a serious complication rate of 2.2 %; mortality rate for sleeve surgeries was exactly zero. The study said that complications were inversely proportional to how many surgeries the hospital handled, and how many surgeries the surgeon had performed. COE status was irrelevant.

http://www.ncbi.nlm....pubmed/20664044