Core Evidence

Levels of Evidence

Editor-in-Chief: Professor Garry Walsh

Levels of Evidence
The validity and quality of evidence is evaluated using a hierarchy of evidence and critical appraisal.

Level
1. Strong evidence from at least one systematic review
2. Evidence from randomized controlled trials
3. Evidence from well-designed trials without randomization, single group pre-/postintervention, cohort, time series, or matched case control studies
4. Evidence from well-designed nonexperimental, observational studies from more than one center or research group
5. Opinions of respected authorities, based on clinical experience, descriptive studies, and reports of expert committees

Adapted from Clark W, Mucklow J. Gathering and weighing the evidence. In: Panton R, Chapman S, editors. Medicines Management. London: BMJ Books and Pharmaceutical Press; 1998.

Synthesis 
The weight, strength, and consistency of the evidence for a drug’s effectiveness on each outcome are evaluated to give a definitive implication for clinical practice wherever possible.

Randomized controlled trials and economic studies are appraised to assess their strengths, weaknesses, and validity. 

Outcomes are selected based on clinical relevance and perceived unmet medical need. Outcome measures are defined as patient-oriented, disease-oriented, or economic.

Conclusions on evidence are summarized as clear, substantial, moderate, limited, or absent depending on a combination of evidence level, its strengths and weaknesses, and its consistency.

Download the Core Evidence template here