Everyday clinical practice is characterised by wide variations that cannot be explained by illness severity or patient preference. Professor Wennberg examines the causes for these variations and suggests ways to remedy the situation

Academic medicine has had only limited success in improving the scientific basis of everyday clinical practice, even within the walls of its own hospitals. Patterns of practice among academic medical centres—as among other institutions—are often idiosyncratic and unscientific, and local medical opinion and local supply of resources are more important than science in determining how medical care is delivered. In short, after nearly 100 years of academic medicine as we know it, much of medicine in the United States remains empirical.

The evaluative clinical sciences—those disciplines whose role in medicine is to evaluate medical theory, understand patient preferences, and improve systems—are capable of improving the scientific basis of clinical practice and warrant high priority in the national research agenda and full adoption into medical school curriculums. These sciences are essential to the development of organised healthcare systems in the 21st century, not least because they expose unwarranted variations in care and can be used to remedy them.

I will begin with a summary of the facts of unwarranted variations in clinical practice, derived from the Dartmouth Atlas of Health Care project, a US national study of traditional (fee for service) Medicare. The atlas project reports on the rates of …