Personally can't see why more mistakes are made in July unless the senior resident isn't as attentive to the intern's actions as I am. Not saying that my interns didn't make mistakes because in medicine it's really one of the best ways we learn but I don't think it's any worse in July as it is in June. If anything I would look at June's numbers because by then the seniors have already begun checking out & the interns think they know everything.
The July effect
It has always been widely publicized that the worst time to go into the hospital was the month of July because of the new interns & residents that were now roaming the hallways of hospitals everywhere. I'm in my third year now having "survived" two July months, one as an intern & the other as the "senior". I can definitely say I was as equally terrified both times. When I was an intern every call, page or order scared me because I was finally directly responsible for a strangers well being & that fear pretty much lasted till November. As the "senior" resident I had to watch not only every order I did but my intern's as well. Dealing with the many type A personalities in medicine I tried not to hover over my interns so most of my supervision was always from afar but best believe there wasn't an order they did that I didn't know about. Just a year removed & the fear to make sure both our patients were able to walk out the hospital was terrifying enough for me.