Levels of Evidence

Select an evidence rating scale to display detailed information.

• Centre for Evidence-Based Medicine, Oxford (1a-5)
• SORT: Strength-of-Recommendation Taxonomy (A,B,C)
• GRADE: Grading of Recommendations Assessment, Development and Evaluation (A,B,C,D)
• Practice Guidelines rating scales (various)

Key to interpretation of practice guidelines

Agency for Healthcare Research and Quality:

A:	There is good research-based evidence to support the recommendation.
B:	There is fair research-based evidence to support the recommendation.
C:	The recommendation is based on expert opinion and panel consensus.
X:	There is evidence of harm from this intervention.

USPSTF Guide to Clinical Preventive Services:

A:	There is good evidence to support the recommendation that the condition be specifically considered in a periodic health examination.
B:	There is fair evidence to support the recommendation that the condition be specifically considered in a periodic health examination.
C:	There is insufficient evidence to recommend for or against the inclusion of the condition in a periodic health examination, but recommendations may be made on other grounds.
D:	There is fair evidence to support the recommendation that the condition be excluded from consideration in a periodic health examination.
E:	There is good evidence to support the recommendation that the condition be excluded from consideration in a periodic health examination.

University of Michigan Practice Guideline:

A:	Randomized controlled trials.
B:	Controlled trials, no randomization.
C:	Observational trials.
D:	Opinion of the expert panel.

Other guidelines:

A:	There is good research-based evidence to support the recommendation.
B:	There is fair research-based evidence to support the recommendation.
C:	The recommendation is based on expert opinion and panel consensus.
X:	There is evidence that the intervention is harmful.