Evidence-Based Practice

Levels of Evidence

Levels of evidence are determined by the following:

1. Strength of Evidence: Confidence that the evidence is a true measure
2. Quality of Evidence: Minimization of bias
3. Statistical Precision: The degree of certainty about the existence of a true measured effect
4. Size of Effect: How much of an effect is above 'No Apparent Effect' for clinically relevant benefits (no harms)
5. Relevance of Evidence: Appropriateness of the outcome measure; usefulness in measuring benefits / harms

Categorizing Evidence

Higher Levels of Evidence

The highest level of evidence is a systematic review of all relevant randomized controlled trials (RCTs). The next highest level of evidence would be at least one RCT on effectiveness. And so on... e.g. a pseudo-randomized trial  that assigns participants by alternating between groups by date of admission.

Lower Levels of Evidence

Non-randomized studies with control group running concurrently with intervention group, non-randomized studies with intervention effects which are compared to previous / historical information, single-case studies, etc.

The Evidence-Based Practice Pyramid

The EBP pyramid is a visual representation that depicts the quality level of a particular type of evidence — the higher on the pyramid it features, the better the quality. Note: People are fallible, and even though a systematic review or meta-analysis may feature at the top of the pyramid, if it is poorly researched and written, a well-executed lower level of evidence can prove better.

Explanatory Video

Discusses the hierarchy of study types in the method section of a scientific paper.