Quotas for procedures is a very interesting topic. Doctors (in the UK at least) carrying out appendectomies consider a negative appendectomy rate (NAR) of around 20% to be optimum. The NAR being the proportion of appendectomies where it turns out the appendix wasn't the cause of the symptoms.

The reason this is considered optimum is that a doctor hitting 0% NAR (which you might naively assume is best) is most likely being overly conservative and missing some genuine cases of appendicitis, which as we all know can be life threatening if left untreated.