A Medicare portal that shows the statistical methodology used to rate and compare hospitals may not be accurate when it comes to estimating the mortality rate of patients suffering from acute MI (AMI) at smaller hospitals, according to a new study.

The research, conducted by professors at University of Pennsylvania's Wharton School, was published in the Journal of the American Statistical Association. The Hospital Compare portal collects data from Medicare claims and hospitals, which is then processed through a random effects logit model. But in doing so, it shrinks the mortality rates in small hospitals to resemble the national average, suggesting there are fewer deaths than there actually are in those facilities.

"Hospital Compare's finding of average risk at small hospitals is a mistake because the current model is not properly calibrated," said Edward I. George, an author of the study and a professor of statistics at Penn's Wharton School, in a statement. "It's a mistake that has implications for patients."

As the portal stands now, low volume hospitals that perform poorly will appear average, and larger hospitals that perform well will also end up looking average on the portal, making observers underestimate or overestimate a facilities’ quality.

"The underestimation of AMI mortality rates at small hospitals, as seen in Hospital Compare, contradicts previously established research and consistent findings that mortality rates are typically higher at low volume hospitals," said Jeffrey H. Silber, an author on the study and professor of pediatrics at the Children's Hospital of Philadelphia, in a statement.

Since viewing the findings on the Medicare portal, the researchers propose replacing the current algorithm will one that includes hospital volume, nursing staff, medical residents and the hospital’s ability to perform cardiovascular procedures into the calculation process. The researchers believe this would yield more accurate and appropriate data on hospitals.

"Patients deserve to have the most accurate information available so they can make well-informed healthcare decisions. Our analysis demonstrates that further modeling with additional hospital attributes has the clear potential to shed more light on the rankings of such hospitals," the authors wrote in the study.