A group of researchers are further disproving medicine’s “July phenomenon”—the myth that clinical care suffers in the summertime due to an influx of new hospital residents—with a study of nearly one million acute ischemic stroke patients.

More than 30,000 physicians start their residency training each July 1, marking the beginning of the academic year in teaching hospitals across the U.S. These arrivals are met with an equal, or larger, number of exits when more experienced doctors leave their posts. The ebb and flow of the process has for years led to a presumption of reduced care quality and medical productivity during the summer months, as well as compromised patient safety and clinical outcomes.

“These new doctors, or trainees, [are caring] for their first patients, usually at different hospitals than they did their medical school, internship or fellowship,” a Mayo Clinic article reads. “They are busy learning new electronic health record systems, clinical care protocols, meeting new people and sometimes doing rotations in areas other than their interest and specialty.”

The phenomenon is one well-rooted in both the medical community and the general public, Joshua Z. Willey, MD, MS, and colleagues wrote in the Journal of the American Heart Association. Still, in spite of studies proving the existence of such a period, little information exists on how it affects acute ischemic stroke patients.

“Inexperienced physicians could potentially impact outcomes in ischemic stroke, including by delays in diagnosis and treatment,” Willey and co-authors wrote.

The researchers analyzed data from 967,891 ischemic stroke patients at 1,625 hospitals in the United States, all of which were participating in the American Heart Association’s Get With the Guidelines—Stroke program. They studied the effects of each academic quarter—the first starting in July and lasting through September—on stroke patients’ treatment and outcomes during the half-decade between January 2009 and December 2013.

Willey et al. focused on door-to-needle time (DTN), door-to-computerized tomography time (DTC), symptomatic intracranial hemorrhage and defect-free care in stroke performance measures (DFC) as the main variables in their study, since they wrote these factors most greatly influence a stroke patient’s quality of care and can identify gaps in proper treatment.

There was no evidence that delays in diagnosis, treatment with thrombolytic therapy, increase in complications or decrease in quality of care were found throughout the year, the authors reported. Though they did find statistically significant differences in distribution of stroke mortality, discharge to home, length of stay, DTC, DTN, DFC, statin use and prophylaxis across academic quarters, the differences were “small, not clinically significant, and not readily attributable to the influx of new physicians in training in teaching hospitals.”

The changes could be explained by a number of things, Willey and colleagues wrote, including something as simple as weather changes, or increased pollution in surrounding areas.

Though their report couldn’t corroborate evidence of a “July phenomenon,” the researchers said their results were consistent with other reports in neurology, obstetrics, critical care, internal medicine, neurosurgery and trauma surgery in discrediting the existence of one.

“We found no evidence of the ‘July phenomenon,’” the authors wrote. “The quality of care provided for acute ischemic stroke is the same regardless of when patients present to the hospital.”