The USPSTF updated its definition of and suggestions for practice for the grade C recommendation. This new definition applies to USPSTF recommendations voted on after July 2012
- Level A
- Good scientific evidence suggests that the benefits of the clinical service substantially outweigh the potential risks. Clinicians should discuss the service with eligible patients.
- Level B
- At least fair scientific evidence suggests that the benefits of the clinical service outweighs the potential risks. Clinicians should discuss the service with eligible patients.
- Level C
- At least fair scientific evidence suggests that there are benefits provided by the clinical service, but the balance between benefits and risks are too close for making general recommendations. Clinicians need not offer it unless there are individual considerations.
- Level D
- At least fair scientific evidence suggests that the risks of the clinical service outweighs potential benefits. Clinicians should not routinely offer the service to asymptomatic patients.
- Level I
- Scientific evidence is lacking, of poor quality, or conflicting, such that the risk versus benefit balance cannot be assessed. Clinicians should help patients understand the uncertainty surrounding the clinical service.
Oxford Center for Evidence-based Medicine levels of evidence (since 2009)
- 1a: Systematic reviews (with homogeneity) of randomized controlled trials
- 1b: Individual randomized controlled trials (with narrow confidence interval)
- 1c: All or none randomized controlled trials
- 2a: Systematic reviews (with homogeneity) of cohort studies
- 2b: Individual cohort study or low quality randomized controlled trials (e.g. <80% follow-up)
- 2c: "Outcomes" Research; ecological studies
- 3a: Systematic review (with homogeneity) of case-control studies
- 3b: Individual case-control study
- 4: Case series (and poor quality cohort and case-control studies)
- 5: Expert opinion without explicit critical appraisal, or based on physiology, bench research or "First Principles"