Epidemiology for Public Health Practice 5th Edition by Robert Friis,Thomas Sellers

Exercise 8

Surgeons at hospital A report that the mortality rate at the end of a 1-year follow-up after a new coronary bypass procedure is 15%. At hospital B, the surgeons report a 1-year mortality rate of 8% after the same procedure. Before concluding that the surgeons at hospital B had vastly superior skill, which of the following possible confounding factors would you examine?
A) the severity (stage) of disease of the patients at the two hospitals at baseline
B) the start of the one-year follow-up at both hospitals (after operation versus after discharge)c. differences in postoperative care at the two hospitals
D) equality of follow-up for mortality
E) all of the above