Evidence ranking schemes have been used for decades and were introduced primarily to help clinicians and other researchers appraise the quality of evidence for therapeutic effects. There are a number of different schemes available today, each using a slightly different approach. They may prioritize study types such as randomized trials over observational studies, and may use other qualities to upgrade or downgrade a particulat study. Each of the examples below provides one such approach.
What is GRADE? From BMJ Best Practice
GRADE (Grading of Recommendations, Assessment, Development and Evaluations) is a transparent framework for developing and presenting summaries of evidence and provides a systematic approach for making clinical practice recommendations.
GRADE has four levels of evidence – also known as certainty in evidence or quality of evidence: very low, low, moderate, and high. Evidence from randomized controlled trials starts at high quality and, because of residual confounding, evidence that includes observational data starts at low quality. The certainty in the evidence is increased or decreased for several reasons. Read additional details on the BMJ site.
GRADE certainty ratings
| Certainty | What it means |
| Very low | The true effect is probably markedly different from the estimated effect |
| Low | The true effect might be markedly different from the estimated effect |
| Moderate | The authors believe that the true effect is probably close to the estimated effect |
| High | The authors have a lot of confidence that the true effect is similar to the estimated effect |
The Oxford Centre for Evidence-Based Medicine uses a 5-Step (Level) grid system to rank studies.
Download the Levels of Evidence document (v2.1, PDF)
The Levels of Evidence table is intended to be used alongside the Introductory Document and Background Document. The CEBM website strongly cautions against reading the table separately. Rather, read the Introductory Document and Table together.
DynaMed provides easy-to-interpret Level of Evidence labels so users can quickly find and determine the quality of the best available evidence. Evidence may be labeled in one of three levels:
Level 1 (likely reliable) Evidence
Representing research results addressing clinical outcomes and meeting an extensive set of quality criteria which minimizes bias.
There are two types of conclusions which can earn a Level 1 label: levels of evidence for conclusions derived from individual studies and levels of evidence for conclusions regarding a body of evidence.
Level 2 (mid-level) Evidence
Representing research results addressing clinical outcomes, and using some method of scientific investigation, but not meeting the quality criteria to achieve Level 1 evidence labeling.
Level 3 (lacking direct) Evidence
Representing reports that are not based on scientific analysis of clinical outcomes. Examples include case series, case reports, expert opinion, and conclusions extrapolated indirectly from scientific studies.
Grades of Recommendation
Guideline producers are now frequently using classification approaches for their evidence and recommendations, and these classifications are recognized and requested by guideline users. When summarizing guideline recommendations for DynaMed users, the DynaMed Editors are using the guideline-specific classifications and providing guideline classification approach when this is done.