Where your ambulance turns during an emergency could be the difference between life and death. That’s because a study has found large gaps in treatment quality at different hospitals around the country.

The report in PLOS One used data from millions of patients at health care facilities across the United States and found that on average, patients were twice as likely to die in the worst hospitals than patients in the best hospitals. That gap was even wider when it came to different aspects of patient safety like catheter-related bloodstream infections. The researchers called for more investigation into the matter.

Read: How To Reattach a Severed Limb

Although the study kept hospital identities confidential, the widespread differences challenge people’s assumptions about their local facilities. “Fundamentally, there is sort of an implicit assumption that every hospital is the same,” Dr. Barry Rosenberg, the study’s lead author and a partner at the Boston Consulting Group in Chicago, told the New York Times. But patient outcomes vary even within a single hospital — “Even a hospital that had excellent outcomes for heart care might have poor outcomes in treating diabetes,” the Times says.

The differences in quality were not always divided based upon the economics of their neighborhoods. “Through the comprehensive risk adjustment of this study, we find select U.S. hospitals serving complex and disadvantaged patient populations that deliver outstanding risk-adjusted outcomes,” the study notes. “Conversely, we find select US hospitals serving relatively healthy and wealthy patients that deliver lagging risk-adjusted outcomes.”

The New York Times listed other factors in a hospital’s performance apart from patient wealth, like the skill of the medical professionals as well as “the culture at the hospital and how they chose to treat a given illness.” And while there were exceptions, the hospitals with more patients generally did better than those with fewer patients.

Source: Rosenberg BL, Kellar JA, Labno A, et al. Quantifying Geographic Variation in Health Care Outcomes in the United States before and after Risk-Adjustment. PLOS One. 2016.

See also:

Fake Blood Powder Can Save Lives In Emergencies

Male vs. Female Surgeons and Music in the Operating Room