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Hospital rankings dramatically affected by calculation methods

October 9, 2012 Toronto

Hospital readmission rates have often been reported as a quality of care indicator. But new research done at the Institute for Clinical Evaluative Sciences (ICES) and the Ottawa Hospital Research Institute (OHRI) shows that the manner in which these rates are calculated can dramatically influence their value and consequent hospital ranking.

“Hospital-specific readmission rates have been reported as a quality of care indicator but no consensus exists on how these should be calculated. Our results highlight that caution is required when comparing hospital performance based on 30-day or urgent readmissions,” says Dr. Carl van Walraven, lead author of the study, scientist at ICES@uOttawa, senior scientist at Ottawa Hospital Research Institute (OHRI) and associate professor at the University of Ottawa (uOttawa).

The study calculated hospital-specific 30-day death or readmission rates for all Ontario hospitals between 2005 and 2010 using different methods for confounder adjustment (age-sex vs. complete) and different units of analysis (all hospitalizations vs. one per patient). It found:

  • Hospital-specific rankings varied extensively.
  • Ranking changed based on which methodology was used.
  • Readmission rates adjusted for age-sex alone had the greatest variation.
  • Notable variation in 30-day death or urgent readmission rates based on how they were calculated.
  • Slight changes in the methods used to calculate hospital-specific readmission rates have a large influence on their values and the consequent hospital rankings.

"We found that slight changes in the methods used to calculate hospital-specific readmission rates had large influences on their values and the consequent hospital rankings, this should be kept in mind when comparing hospital performance using readmission rates,” says van Walraven.

Authors: Carl van Walraven, Jenna Wong, Steven Hawken and Alan J. Forster.

The study “Hospital-specific death or urgent readmission rates vary extensively based on the methods used to calculate them,” is in the current issue of the CMAJ.

ICES is an independent, non-profit organization that uses population-based health information to produce knowledge on a broad range of health care issues. Our unbiased evidence provides measures of health system performance, a clearer understanding of the shifting health care needs of Ontarians, and a stimulus for discussion of practical solutions to optimize scarce resources. ICES knowledge is highly regarded in Canada and abroad, and is widely used by government, hospitals, planners, and practitioners to make decisions about care delivery and to develop policy.

The Ottawa Hospital Research Institute (OHRI) is the research arm of The Ottawa Hospital and is an affiliated institute of the University of Ottawa, closely associated with the university’s faculties of Medicine and Health Sciences. OHRI includes more than 1,700 scientists, clinical investigators, graduate students, postdoctoral fellows and staff conducting research to improve the understanding, prevention, diagnosis and treatment of human disease. Research at OHRI is supported by The Ottawa Hospital Foundation.

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