The health care systems of developed countries share common problems. Firstly, the explosion of costly medical technologies increasingly jeopardises our ability to give everybody all the care that would benefit them. And, secondly, the explosion in medical services has made it virtually impossible to remember the indications, complications, and costs of procedures and drugs - that is, to practise good medicine without additional help.

Studies of appropriateness underline the seriousness of these problems. By appropriate care I mean that for which the benefits exceed the risks by a wide enough margin to make it worth providing. If we could increase appropriate and decrease inappropriate care, the benefits to patients and society in terms of health and wealth would be enormous. Indeed, without methods to detect inappropriate care, society's ability to maintain universal insurance coverage may disappear.1

But how do you measure the appropriateness of care?2 Although the clinical literature is the place to start, it mostly …