With practice, physicians often become better at their jobs. It’s not too surprising. Studies have found veteran surgeons typically have better outcomes than their less experienced colleagues. The trend applies for most procedures.

Recently, Nikhil R. Sahni, of Harvard University and McKinsey & Co., and his colleagues took the research a step further. They wondered if specialization was more important than volume and evaluated 25,152 surgeons who performed one of eight common procedures on 695,987 Medicare beneficiaries from 2008 to 2013.

As they noted, the specialization hypothesis would mean a surgeon who performed 20 procedures of which all 20 are valve replacements would have better outcomes than a surgeon who performed 100 procedures, of which only 40 are valve replacements. The volume hypothesis would suggest the opposite, that the doctor with 40 valve replacement surgeries would achieve more success than the one with 20.

It turns out that for many common procedures, specialization was more important than volume. The results, which were published in BMJ on July 21, showed that surgeons in the top quarter of specialization for carotid endarterectomy, CABG, valve replacement and abdominal aortic aneurysm repair had a significant relative risk reduction in operative mortality compared with those in the bottom quarter of specialization.

The relative risk reduction in 30-day operative mortality between the bottom and top quarters of surgeon specialization was 15 percent with CABG, 28 percent with carotid endarterectomy, 42 percent with abdominal aortic aneurysm repair and 46 percent with valve replacement.

Further, for carotid endarterectomy and valve replacement, patients had a greater relative risk reduction in mortality if they chose a doctor in the top quarter of surgeon specializations compared with a doctor in the top quarter of procedure-specific volume.

“The observed specialization-outcomes relation suggests a new, easily measured metric of surgeons’ quality that builds on the volume-outcomes relation to inform the way healthcare is organized and delivered,” the researchers wrote.

Sahni and his colleagues offered potential reasons for the association between specialization and outcomes. By repeating tasks, surgeons who specialize in one procedure may improve their muscle memory and dexterity and become more familiar with medical devices.

The researchers made clear that they could not claim that specialization caused an improvement in outcomes. After all, this was a retrospective analysis, and they did not have information on the surgeons’ skills or characteristics or how or why they chose to operate on certain patients. Still, they said the results warrant further research.

“Our findings may have implications for policy makers, administrators, physicians, and patients, especially as surgeons’ specialization is measurable using data available to health systems,” they wrote. “Policy makers considering how to improve the quality of rural or smaller hospitals in which surgeons cannot meet minimal volume thresholds could use surgeon specialization to assign patients to surgeons. At larger facilities, administrators determining case distribution across surgeons might consider not only a given surgeon’s volume in that procedure but also his or her degree of specialization. A physician might use a measure of surgeon specialization to refer his or her patient to the most appropriate surgeon, possibly improving patients’ outcomes. Finally, if these data are made available to a patient, he or she could choose a surgeon who specializes in the relevant procedure to possibly improve his or her chance of survival.”