CMS' Overall Star Ratings methodology does not account for differences in the type and volume of quality measures hospitals share with the agency, which may offer an inaccurate analysis of quality performance, according to a study published in Health Affairs.
CMS requires hospitals to have a minimum number of patient cases to report data for a star ratings measure. As a result, hospitals that treat a larger volume and mix of cases often report more measures than hospitals treating a smaller patient pool. Despite this variation, CMS rates all hospitals on the same one to five star scale, regardless of the type or number of measures reported.
For the study, researchers analyzed data on 3,692 hospitals from the December 2017 star ratings update. Researchers sorted hospitals into three groups based on similarities with the type and volume of measures reported. Group one reported an average of 43 measures, group two reported 36 measures and group three reported just 22 measures.
Researchers found hospitals in the third group often had higher star ratings, while hospitals in the first group had lower scores.
"Patients, referring providers, payers and other stakeholders who use the ratings in their decision-making can be misled if they assume that higher hospital quality is correlated with a higher star rating," the researchers said. They warned against lumping hospitals together for the analysis and instead suggested CMS assess hospitals in groups based on how they report on the quality measures.