Intended for healthcare professionals


Time to tackle unwarranted variations in practice

BMJ 2011; 342 doi: (Published 17 March 2011) Cite this as: BMJ 2011;342:d1513
  1. John E Wennberg, Peggy Y Thomson professor emeritus in the evaluative clinical sciences
  1. 1Dartmouth Institute of Health Policy and Clinical Practice, 35 Centerra Parkway, Lebanon, NH 03766, USA
  1. john.wennberg{at}

US and UK data show that much of the variation in use of healthcare is accounted for by the willingness and ability of doctors to offer treatment rather than differences in illness or patient preference. Identifying and reducing such variation should be a priority for health providers, says John Wennberg

Since Alison Glover’s classic 1938 study showing local differences in rates of tonsillectomy among British schoolchildren,1 health service researchers have documented extensive variation in the delivery of healthcare in many parts of the world.2 3 4 5 Information on practice variation is important for examining the relations between policy decisions and clinical decisions and raises important questions concerning the efficiency and effectiveness of healthcare. I have therefore argued that population based information should be routinely reported6 and, through the Dartmouth Atlas Project, have taken steps to make such information publicly available for care to Americans aged ≥65 years provided through the Medicare programme. The project has highlighted that much of the variation among hospital referral regions in per capita spending, resource allocation, and service use is unwarranted because it isn’t explained by illness or patient preference.7 8

The publication of The NHS Atlas of Variation in Healthcare,9 which compares healthcare delivery among primary care trusts, shows a similar story in England. Below, I consider the relevance of the Dartmouth work for the NHS.

Unwarranted variation and categories of care

In evaluating practice variation, clinical care can be grouped into three categories with different implications for patients, clinicians, and policy makers:10

  • Effective care is defined as interventions for which the benefits far outweigh the risks; in this case the “right” rate of treatment is 100% of patients defined by evidence based guidelines to be in need, and unwarranted variation is generally a matter of underuse.

  • Preference sensitive care is when more …

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