Should the NHS strive to eradicate all unexplained variation? Yes

Medicine is an art informed by science, and the best medicine requires both the art to be well done and the science to be accurate. Every person is different, and variation is inherent to all things. But the NHS should strive to eradicate all unwarranted, unintended, and inappropriate variation.

Donald Berwick wrote the seminal paper on controlling variation in health care in 1991, building on the work of Walter Shewart from the 1930s.1 Berwick refers not to unexplained variation but to unintended variation. Deming recognises two types of variation: common cause (the random variation that occurs in all processes) and special cause (arising from unexpected events or unplanned situations).2 The NHS Institute for Innovation and Improvement refers to “natural variation” and “artificial variation”—again there is no use of the word unexplained.3