i did not read the study. an obvious confounding factor is that doctors with better board scores are hired into better hospitals with better patient populations, and thus better outcomes.
> The researchers compared outcomes for patients within the same hospitals who were cared for by doctors with different exam scores. This allowed the researchers to eliminate, or at least minimize, the effect of differences in patient populations, hospital resources, and other variations that might influence the odds of patient death or readmission, independent of a doctor’s performance.