[samplenoise]

> The effect size of surgeons’ birthday observed in our analysis (1.3 percentage point increase or a 23% increase in mortality), though substantial, is comparable to the impact of other events, including holidays (e.g., Christmas and New Year) and weekends. > But the authors say the “natural experiment” in the present study is more revealing than, for example, holiday-related mortality rates. That is because “those events not only affect physicians’ performance but also influence patients’ decision to seek care (i.e., patients seeking care on these special days might be sicker than those seeking care on other days), as well as hospital staffing.” Unless, of course, the patients know their surgeon’s birthday, which is unlikely (though that may change if this study becomes widely known). That doesn't take exclude the possibility that surgeons may be assigned different patients on their birthdays. Some studies on the 'weekend effect' [1] seem to also control for illness severity, not clear if that was done here. [1] https://en.wikipedia.org/wiki/Weekend_effect