Do clinical practice guidelines define good medical care? The need for good science and the disclosure of uncertainty when defining 'best practices'.

Practice guidelines, although important in promoting quality, can also be harmful if they do not advocate the best options for patients. The latter can occur because of uncertainties in scientific evidence, biases in guideline development, and patient heterogeneity. Guidelines must therefore accurately describe the quality of the evidence and the degree of uncertainty that underlie recommendations. Proper methods for developing practice guidelines are reviewed.