Certificate of need laws hamper hospital quality of care, according to new research.

The laws, which require regulatory approval prior to building a new hospital or other healthcare facilities, remain on the books in 36 states and the District of Columbia. They have often been the subject of fierce debate, drawing fire from anti-regulatory advocates. Two states, Virginia and South Carolina, are currently in different phases of repealing the laws.

Researchers at the Mercatus Center, a think tank located at George Mason University in Virginia, used data from the Hospital Compare database operated by the Centers for Medicare & Medicaid Services and quality measures such as HCAHPS to compare 921 hospitals in CON and non-Con states in nine categories between 2011 and 2015.

“We find that mortality rates for pneumonia, heart failure, and heart attacks are significantly higher in hospitals in CON states relative to those in non-CON states,” the study said. “We also find that deaths from complications after surgery are significantly higher in CON states.” Only the heart attack mortality rates were similar between the CON and non-CON states, according to the study.

The biggest differential was the mortality rate among surgical patients with serious treatable complications. It was 111.1 per 1,000 discharges at non-CON hospitals and 116 per 1,000 at CON hospitals, a differential of about 4.5 percent.

However, the data showed mostly negligible differences in other outcomes, often in the 1 to percent range in terms of differential. The pneumonia mortality rate was 11.8 percent at non-CON hospitals, while it was 12 percent at CON hospitals, a total differential of less than 2 percent,  according to the study.

The study's authors also acknowledged that the impact of the Hospital Readmissions Reduction Program, which began in 2012 and penalized hospitals for excess readmissions, “is not captured in our model.”

A previous study on CON laws concluded that hospitals in non-CON states had slightly lower costs overall.