We use the Grading of Recommendations Assessment, Development and Evaluation (GRADE) to classify synthesized recommendations as Strong or Weak.

Strong recommendations are used when, based on the available evidence, clinicians (without conflicts of interest) consistently have a high degree of confidence that the desirable consequences (health benefits, decreased costs and burdens) outweigh the undesirable consequences (harms, costs, burdens).
Weak recommendations are used when, based on the available evidence, clinicians believe that desirable and undesirable consequences are finely balanced, or appreciable uncertainty exists about the magnitude of expected consequences (benefits and harms). Weak recommendations are used when clinicians disagree in judgments of relative benefit and harm, or have limited confidence in their judgments. Weak recommendations are also used when the range of patient values and preferences suggests that informed patients are likely to make different choices.

Why rate the certainty in the evidence and strength of recommendations?

Judgments about evidence and recommendations in healthcare are complex. For example, those making recommendations about whether or not to recommend a new generation of blood thinners for patients with irregular heart beat (atrial fibrillation) must agree on which outcomes to consider, which evidence to include for each outcome, how to assess the quality of that evidence, and how to determine if blood thinners do more good than harm. Because resources are always limited and money that is allocated to treating atrial fibrillation cannot be spent on other worthwhile interventions, they may also need to decide whether any incremental health benefits are worth the additional costs.

Systematic reviews of the effects of healthcare provide essential, but not sufficient information for making well informed decisions. Reviewers and people who use reviews draw conclusions about the quality of the evidence, either implicitly or explicitly. Such judgments guide subsequent decisions. For example, clinical actions are likely to differ depending on whether one concludes that the evidence that blood thinners reduces the risk of stroke in patients with atrial fibrillation is convincing (high quality) or that it is unconvincing (low quality).

Similarly, practice guidelines and people who use them draw conclusions about the strength of recommendations, either implicitly or explicitly. Using the same example, a guideline that recommends that patients with atrial fibrillation should be treated may suggest that all patients definitely should be treated or that patients should probably be treated, implying that treatment may not be warranted in all patients. A systematic and explicit approach to making judgments such as these can help to prevent errors, facilitate critical appraisal of these judgments, and can help to improve communication of this information.