Seniors in more impoverished areas of the country are significantly more likely to die after surgery than their wealthier neighbors, according to recent research.

Investigators at the University of Michigan analyzed the death rates for 1 million elderly cancer and heart surgery patients. Those in low-income ZIP codes were anywhere between 17% and 39% more likely to die after surgery, according to their findings. Personal income appears not to be a factor, according to the report: all surgical patients in poor areas were more likely to die compared with all patients in rich areas who were less likely to die.

Report authors suggest that hospitals in lower-income areas of the country themselves have fewer resources with which to treat their patients, leading to the higher mortality rate. While previous studies have examined the relationship between income and the outcomes of certain procedures, this is the first to connect socio-economics with a wide range of surgical outcomes, according to lead author Dr. Nancy Birkmeyer, an associate professor of surgery. The report is published in the September issue of the journal Medical Care.