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If all variation were bad, solutions would be easy. The difficulty is in reducing the bad variation, which reflects the limits of professional knowledge and failures in its application, while preserving the good variation that makes care patient centered. When we fail, we provide services to patients who don’t need or wouldn’t choose them while we withhold the same services from people who do or would, generally making far more costly errors of overuse than of underuse.

Mulley AJ. Improving productivity in the NHS BMJ 2010

Variation in the structures, processes, and organization of healthcare services in the United States has been studied for decades. As the field of hospital medicine grows, contributions from hospitalists in the fields of health services research and quality improvement have been instrumental in advancing our understanding of the drivers of variation and the impact of this variation on the cost, quality, and outcomes of care delivered to hospitalized children.


The first population-based study of variation in pediatric healthcare was published by British researcher J. Allison Glover in 1938.1 Starting early in the 20th century, rates of tonsillectomies among school children in England and Wales rose dramatically. By 1931, the surgery made up three-quarters of all procedures performed in children in the United Kingdom. Across boroughs, however, the proportion of children having their tonsils removed varied in some cases by tenfold, even among areas with similar populations. Seeking to understand why these rates were so variable, Glover closely examined the hospital and education health records from several neighboring boroughs and found significant disparities in the rates of tonsillectomy. For example, “well-to-do” vs. poor children were more likely to enter secondary school without their tonsils. However, neither socioeconomic status nor any other health service area or population characteristics explained why a child living in one borough had a higher probability of getting their tonsils removed than a similar child in a different borough. Put simply, Glover concluded that the variation “defie[d] explanation.”

In the 1960s, John Wennberg—then a researcher at the Dartmouth School of Medicine—would refer to this type of unexplained geographic variation as unwarranted, or variation in the utilization of health care services that cannot be explained by patient illness, patient preferences, or evidence, but rather indicates differences in health system performance. Taking advantage of newly implemented health data systems in Vermont and other areas of New England, Wennberg and his colleagues at Dartmouth and Johns Hopkins used advanced statistical methods to analyze patterns in the healthcare utilization among neighboring hospital service areas.2,3 In what was a highly influential series of publications, the Dartmouth group reported wide geographic variation in hospital admissions, diagnostic testing, and surgical procedures—including a tenfold difference in rates of tonsillectomies. All findings were still highly significant after case-mix adjustments, including prevalence of disease, patient demographics, socioeconomic factors, and medical practice differences....

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