At Pajamas Media Dalrymple looks at a recent study on in-flight medical emergencies:
The presence of a physician on board (as there was in nearly half of all flights), or at least of one who came forward to give assistance, made it more likely that an aircraft would be diverted to the nearest airport. Oddly enough, the patient was no more likely to be hospitalized on arrival after assistance by a doctor than when there was no doctor on board, suggesting that doctors on board had either cured their patients by the time of landing, or tended to overestimate the seriousness of the cases. Oddly enough, passengers who were assisted by flight attendants were considerably less likely to cause the aircraft to divert or to be hospitalised on arrival. The authors do not try to explain and make no comment on this.