One of my favorite parts of residency is working with my co-residents as part of a larger team. From thinking through complicated diagnoses, to hanging out at noon lectures, to simply being together through medicine’s more challenging moments, these positive group dynamics make the job more satisfying. It’s something I hope to preserve beyond my training years.

In today’s Research Corner, I take a deeper look at how being part of a group practice can affect a physician’s prescribing behavior — and what that might mean for patients. I hope you find the results as interesting as I did.

How a Doctor’s Peers Shape Prescribing Habits

Across the U.S., the business of primary care is changing dramatically. More and more doctors are employed by hospitals, insurers or corporations like Amazon and Walmart.

But who physicians work for isn’t the only thing that’s changing. How they work is shifting too.

Forty years ago, about 40% of all types of physicians in the U.S. practiced alone. By 2014, that number had fallen to just 17%. Small group practices are still relatively common, especially in rural areas, but an increasing number of physicians — including many primary care doctors — now work in very large groups.

This evolving practice landscape raises an important question: Does the size of a doctor’s practice affect the care they deliver to patients?

A creative, new NBER working paper shows it could help in at least one way: Practicing in a group might help doctors prescribe opioids more appropriately than when they work alone. 

Opioids and benzodiazepines don’t mix

The study authors — Kate Bundorf, Daniel Kessler and Sahil Lalwani — sifted through prescribing data for about 200,000 primary care doctors serving Medicare patients in 2014 and 2018. Those doctors worked in various settings, from solo practices to large groups with more than a hundred physicians.

The researchers measured the percentage of each doctor’s patients taking benzodiazepines (a type of medication that is used to treat anxiety and seizures) to whom the physician had also prescribed opioids; that’s a potentially lethal combination of prescription drugs that is usually considered inappropriate. The Food and Drug Administration requires the labels of both types of drugs to include black box warnings about the dangers of mixing the medicines.

Evidence suggests that a doctor’s age and whether they have lots of competing practices nearby could impact how likely they are to prescribe opioids. But after taking those factors into account, the researchers still found that physicians who moved from a solo practice during the four-year study period were as much as 20% less likely to prescribe those two medicines in combination than doctors who stayed in solo practice.

How size of a group practice and the age of its members can affect its influence

The size of the group practice also seemed to influence the way the doctors prescribed opioids. Those moving from a solo practice to larger groups showed an 18% reduction in total opioid prescriptions compared to similar physicians who stayed in solo practice. Conversely, physicians transitioning from larger groups to solo practice increased their opioid prescribing by even more than 18%, compared to physicians who stayed in larger groups.

Interestingly, the researchers also found that doctors of any age who moved to a group practice made up of older physicians were more likely to prescribe more frequent or higher doses of opiates, and for a longer duration.

“I wasn’t expecting there to be quite as big of a difference when physicians switched groups,” said Michael Barnett, an assistant professor of health policy at Harvard who was not involved in the study. “It certainly makes me think that peer effects play a bigger role in prescribing behavior than I might have thought.”

Why group size affects prescribing — and its impact on quality of care — is still unclear

The study leaves some big questions unanswered, Barnett says. For example, “What exactly does it mean clinically that physicians are prescribing more or fewer opioids?”

Certain groups of vulnerable patients have historically been underprescribed opioids, he notes, and a tendency to overlap prescriptions of benzodiazepines and opioids is only one measure of the quality of care a doctor provides.

Still, the large size of this group effect raises another concern: What’s driving it?

There are no firm data yet on that score, but both Barnett and Kate Bundorf, one of the study’s authors, offered some guesses when we spoke. It’s possible, they said, that physicians working in larger groups have more opportunities to discuss clinical evidence with their colleagues — and this could lead to prescribing habits more in line with the standard of care. 

Larger practices may also have more resources to invest in quality improvement initiatives — such as electronic medical record alerts and performance dashboards — that could help clinicians quickly find and fix weak spots in their prescribing habits.

Important questions remain around how to best support solo practice doctors

The findings certainly don’t condemn small medical practices. For one thing, large group practices have downsides too: They are often the result of market consolidation — as hospitals and big health care networks merge — and that can drive up the cost of care for patients. Also, there are a variety of personal and professional reasons that a physician may choose to stay in a smaller practice setting. In rural areas, for example, where the size of the population may not be big enough to support large practices, solo practices and small groups will continue to be the rule.

As long as 50% of the country’s doctors continue to work in small practice settings, this study does raise worthwhile questions about how to best support them with some of the benefits of groups — like helping them network with peers, for example, or creating incentives to avoid dangerous prescription combinations — without forcing them to upsize.