The July effect, sometimes referred to as the July phenomenon, is a perceived increase in the risk of medical errors and surgical complications that occurs in association with the time of year in which United States medical school graduates begin residencies. A similar period in the United Kingdom is known as the killing season.
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In the United States
A Journal of General Internal Medicine study, published in 2010, investigated medical errors from 1979 to 2006 in United States hospitals and found that medication errors increased 10% during the month of July at teaching hospitals, but not in neighboring hospitals. Surgical errors did not increase, leading to the hypothesis that medication errors are easier for new personnel to make because they are prescribing drugs on their own, rather than being cross-checked by others. The study did not have sufficient data to link the increased errors to new residents, however, and further study would need to be done in order to determine the sources of this increase. A criticism of the study suggests that the supervision of new residents and the patient loads at teaching hospitals have improved since 1979 and that the results may be skewed by including much older data.
Other studies searching for the July effect have found variable evidence of an increased risk, with several studies finding no risk at all.
In the United Kingdom
In Britain, there is an influx of newly qualified doctors into the National Health Service (NHS) each August, and this period is associated with an increase in medical errors. The phenomenon has been recognised by Professor Sir Bruce Keogh, medical director of the NHS. The term "Killing Season" originated in the 1994 British medical drama series Cardiac Arrest written by Jed Mercurio (under the pseudonym John MacUre). In an episode first broadcast on BBC1 on 5 May 1994, the character Dr. Claire Maitland consoles a junior who has just committed a fatal error with the dialogue: "You come out of medical school knowing bugger all. No wonder August is the killing season. We all kill a few patients while we're learning."
The day when junior doctors typically start work has also been dubbed "Black Wednesday" among NHS staff. A 2009 Imperial College London study of records for 300,000 patients at 170 hospitals between 2000 and 2008 found that death rates were 6 percent higher on Black Wednesday than the previous Wednesday. The study also found that typically fewer patients attended A&E on the first Wednesday in August than the previous week.