Via Andrew Sullivan, the chart on the right shows the relative odds of dying after elective surgery depending on the day of the week the surgery was done. Apparently doctors and staff are bright-eyed and bushy-tailed on Monday, but not so much on Friday. Or maybe it has to do with staffing levels. The authors conclude that it's all very mysterious: "The reasons behind this remain unknown, but we know that serious complications are more likely to occur within the first 48 hours after an operation, and a failure to rescue the patient could be due to well known issues relating to reduced and/or locum staffing (expressed as number and level of experience) and poorer availability of services over a weekend."
Anyway, this is just England. There's nothing to worry about here in America, I'm sure. All the same, maybe you want to schedule your next knee replacement for a nice lazy Tuesday, eh?