Chicago Hospital Finds Glitch in Medicare’s Hospital Compare Statistical Calculations

After officials at Rush University Medical Center noted a sharp drop in its quality ratings by the Centers for Medicare and Medicaid Systems (CMS), an internal analysis revealed that CMS has been using faulty math to calculate the agency’s star ratings since 2016.

Back in May, the Chicago-based academic medical center learned that it had fallen from a five-star rating—which is the highest rating given—down to three stars. CMS uses the controversial stars-based rating system on its Hospital Compare website. According to a report in Modern Healthcare, with whom Rush shared its own statistical analysis—a recreation of CMS’ statistical model—CMS officials brushed off Rush’s concerns. CMS gives providers two months to review their ratings before they are published on Hospital Compare.

However, when quality officials at Rush recreated the CMS statistical model for the rating system, it found that the CMS formula relied heavily on the measure for PSI-90 for the first four releases of the ratings and then complication rates from hip and knee replacements for the latest release. Rush’s analysis found that one measure, PSI-90, accounted for about 98 percent of a hospital’s performance in the safety group.

This rating system calculates stars by weighting provider performance in seven areas: mortality, safety of care, readmission, patient experience, effectiveness of care, timeliness of care, and efficient use of medical imaging—with certain categories, such as safety, weighted higher. Rush’s statistics, however, found that the weight given to PSI-90 safety measure was much greater than the seven other measures, and even higher than for measures for catheter-associated urinary infections and central line infections, Modern Healthcare reports.

The safety scores are particularly important to hospitals because both consumers and payers look at a hospital’s safety score when factoring reimbursement and physician selection for lucrative joint replacement procedures. Modern Healthcare speculates that Rush’s own analysis likely contributed to the decision by CMS to postpone the July release of its annual star ratings. Quality officials at UChicago Medicine, the University of Virginia Health System, and the Association of American Medical Colleges also contributed to Rush’s calculations.

Mary Butler is the associate editor at Journal of AHIMA.

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