Users' Guides to the Medical Literature

THE ULTIMATE PURPOSE of applied health research is to improve health care. Summarizing the literature to adduce recommendations for clinical practice is an important part of the process. Recently, the health sciences community has reduced the bias and imprecision of traditional literature summaries and their associated recommendations through the development of rigorous criteria for both literature overviews^1-3and practice guidelines.^4,5Even when recommendations come from such rigorous approaches, however, it is important to differentiate between those based on weak vs strong evidence. Recommendations based on inadequate evidence often require reversal when sufficient data become available,⁶while timely implementation of recommendations based on strong evidence can save lives.⁶In this article, we suggest an approach to classifying strength of recommendations. We direct our discussion primarily at clinicians who make treatment recommendations that they hope their colleagues will follow. However, we believe that any clinician who attends to