(Time.com) -- "Don't get sick in July."
This is a common refrain in teaching hospitals. It's driven by the academic calendar: July is when the new interns — fresh out of medical school — start work. It's also when the senior trainees, the residents and fellows, graduate to supervisory, self-managed patient care roles.
In other words, it's when everyone is most inexperienced. The worry is that this inexperience leads to mistakes.
But what is less clear is how a doctor's experience influences the quality of their care. On its face, it makes sense that the longer a doctor practices, the more expertise she gains — which means better care for you.
But, in reality, it's not that simple.
Say, for instance, your doctor tells you: "In my experience, this antibiotic works great for sinus infections." Fair enough. It may also be completely true from your doctor's perspective: When she has prescribed antibiotics in the past for sinus infections, patients got better. But statements like this make us cringe, for two reasons.
First, as it turns out, antibiotics don't actually work for most sinus infections. In a large study published in the Journal of the American Medical Association earlier this year, people with sinusitis were randomly assigned to take antibiotics or a placebo. People treated with antibiotics did no better than those who got the sugar pill. The reason that bacteria-killing antibiotics don't help when you have sinusitis is because the infection is almost always caused by a virus.
The second — and perhaps more cringe-worthy — part is the summoning of the phrase "in my experience" as the major reason to prescribe the drug.
In the case of sinus infections and antibiotics, doctors' experiences (and those of patients) support the wrong decision. Here's why: The natural course of most sinus infections is to resolve on their own over time. People tend to go to the doctor — and get their antibiotics — when they are at their sickest. So they and their doctors falsely attribute their improvement to the antibiotic pills. Here, experience gets in the way of the right medical decision, which is to avoid antibiotics in the first place.
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So let's get back to the July effect and the inexperienced, error-prone interns.
On one hand, some studies suggest that the July effect is a myth: A recent study examining 10 years of data on patients undergoing neurosurgery showed that July was no more dangerous than other months. On the other hand, reports have found that July patients do indeed fare worse: In a study of patients undergoing surgery for spine-related cancer, July patients were more than twice as likely to have a surgical complication and 81% more likely to die, compared with August or June patients.
A recent systematic review of all the research done on the topic concluded that many of the studies showing no July effect had small sample sizes and were not rigorously done, but the bigger and better investigations leaned toward finding that July is truly a more dangerous month in teaching hospitals.
So is medical experience good or bad?
Well, in most cases, your doctor's experience is very helpful, allowing her to pick up on a very subtle symptom early in a disease process, for instance, or to determine the right treatment when your condition falls outside of what is taught in textbooks.
And for many medical treatments — especially the highly technical ones — there's a direct correlation between physician experience (the number of procedures she's performed) and your outcome (whether the procedure works).
In a variety of situations, though, experience can backfire, and the reason is simple psychology. Doctors are human too, and they fall prey to tricks of the mind — like thinking that an ineffective treatment really works (ahem, antibiotics for sinus infections).
In fact, entire fields of research are devoted to understanding why these errors of thought occur. They spring from so-called cognitive biases and false heuristics: mental shortcuts that can mislead even highly educated, well-seasoned practitioners into making the wrong decisions.
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Here are four key cognitive biases that trick even the smartest physicians:
Anchoring bias, which causes doctors to lock onto a diagnosis early and disregard new and conflicting information. For example, a patient may be diagnosed with a quickly fatal cancer, but then ends up trying various (ineffective) herbal remedies and lives for 30 more years. Instead of considering whether the initial diagnosis was incorrect, the patient — and maybe even the doctor — may falsely assume that the herbal remedies cured the cancer.
Availability bias, when clinicians tend to think that the patient they are treating today has the same condition as the patient they treated last week. Imagine your doctor saw a rare, life-threatening illness last week that presented with a common symptom, such as belly pain. Today, you're in the doctor's office for belly pain, and your doctor may be unjustifiably concerned that you too have that rare life-threatening disease just because she's still thinking about it.
Confirmation bias, which causes doctors to believe evidence when it supports their pre-conceived opinion, while ignoring evidence that contradicts it. For example, let's say your doctor is pretty certain that you have an infection and orders a test to confirm the suspicion. The test is negative for infection, but she treats you for it anyway because she doesn't believe the test results; meanwhile, she disregards clues that point to another, correct diagnosis.
Commission bias, when doctors err on the side of doing something — like ordering a prostate biopsy — as opposed to watchful waiting because it seems that doing something is better than a doing nothing.
As you can imagine, the effects of these biases can be significant, particularly if it leads to the wrong treatment or a wrong diagnosis. In the case of antibiotics for sinusitis, for instance, the negative impacts of overtreatment include the promotion of drug-resistant superbugs, higher medical spending and rare but sometimes serious allergic reactions to antibiotics.
So when does experience help and when does it get the way?
That's a tough question because there are clearly many benefits to having a highly experienced doctor, such as technically proficiency and knowing the pitfalls of various treatments. Conversely, there may actually be some intangible benefits to having a less experienced doctor: She may have a more up-to-date education, boundless energy and perhaps less susceptibility to cognitive biases developed by years of thinking and practicing the same way.
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The key here lies in the evidence. The data show that certain procedures have a clear volume-outcome relationship — that is, the more experience a doctor or hospital has, the better their outcomes.
These procedures include: open-heart surgery, hernia repairs, obstetrics and trauma care. Note that many of the areas where the volume-outcome relationship exists involve technical expertise. As Malcolm Gladwell so popularly noted in his book "Outliers," Andre Agassi got good at tennis through 10,000 hours of practice. The same principle holds with doctors who perform medical procedures.
The flip side involves certain medical situations in which medical evidence trumps experience, such as using routine mammograms to screen for breast cancer in women under 50, prescribing anti-arrhythmia medications for heart rhythm disturbances after heart attack, or adhering to super-tight glucose control in diabetics.
In all these cases, as new evidence emerged refuting the benefits of what had once been considered standard care, both doctors and patients were shocked into re-thinking treatment decisions. Here, what seemed to make sense from years of experience turned out to be wrong.
So what can you do as a patient to receive the best care? Well, maybe nothing if you get admitted on an emergent basis to a teaching hospital during July. But one thing you should always do is ask a lot of questions. It may not always be possible to determine that your doctor has fallen victim to an unconscious thinking trap or that she's practicing outdated medicine. But asking questions does force your doctor to think and justify decisions about your care.
Secondly, become an informed patient: Try to learn as much as you can about your medical issues and what trusted sources recommend as the "right" approach. Even 15 years ago, it was rare for a patient to crack open a medical textbook to question a treatment decision. Now, online resources such as MedlinePlus, provide both up-to-date and easy-to-understand explanations of complex medical care. A good summary of evidence-based medicine can also be found at the Agency for Healthcare Research and Quality's website.
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To be clear, an experienced doctor may provide the best care in the world for you or your loved one. But for some decisions, you'd be better off if she didn't use that experience as the only reason to choose a medicine or test. Experience may make the mechanics of a medical procedure smoother and more efficient, but it can also make medical decision-making messy, and sometimes plain wrong.
Meisel is an assistant professor of emergency medicine at the Perelman School of Medicine and medical editor of the LDI Health Economist, both at the University of Pennsylvania. Follow him on Twitter at @zacharymeisel.
Pines is the director of the Center for Health Care Quality and an associate professor of emergency medicine at George Washington University. Follow him on Twitter at @DrJessePines.
This article originally appeared on Time.com:
The 'July effect' revisited: Why experienced doctors may not deliver the best medical care
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