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Evidence Based Practice Toolkit

Levels of Evidence / Evidence Hierarchy

Levels of evidence (sometimes called hierarchy of evidence) are assigned to studies based on the research design, quality of the study, and applicability to patient care. Higher levels of evidence have less risk of bias

Levels of Evidence (Melnyk & Fineout-Overholt 2023)

Level of Evidence


Level 1

Evidence from a systematic review or meta-analysis of all relevant RCTs (randomized controlled trials).

Level 2

Evidence from at least one well-designed RCT (e.g. large multi-site RCT).

Level 3

Evidence from a single well-designed controlled trials without randomization (aka quasi-experimental studies) OR a systematic review of a complete BOE (integrative review of higher and lower evidence) OR mixed methods intervention studies 

Level 4

Evidence from well-designed case-control or cohort studies

Level 5

Evidence from systematic reviews of descriptive and qualitative studies (meta-synthesis)

Level 6

Evidence from a single descriptive or qualitative study, EBP, EBQI and QI projects

Level 7

Evidence from the opinion of authorities and/or reports of expert committees, reports from committees of experts and narrative and literature reviews














*Adapted from: Melnyk, & Fineout-Overholt, E. (2023). Evidence-based practice in nursing & healthcare: A guide to best practice (Fifth edition.). Wolters Kluwer.

Levels of Evidence / Evidence Hierarchy

Levels of Evidence (LoBiondo-Wood & Haber 2022)


Research Designs

1 Systematic Review or meta-analysis of RCTs (randomized control trials)
2 Randomized control trials 
3 Quasi-experimental Studies
4 Non-experimental studies
5 Meta-synthesis
6 Qualitative studies
7 Expert opinions: reports from expert panels and organizations, not based on research

Adapted from LoBiondo-Wood, G. & Haber, J. (2022). Nursing research: Methods and critical appraisal for evidence-based practice (10th ed.). Elsevier.

Evidence Pyramid (Levels of Evidence)

Evidence Pyramid

"Evidence Pyramid" is a product of Tufts University and is licensed under BY-NC-SA license 4.0

Tufts' "Evidence Pyramid" is based in part on the Oxford Centre for Evidence-Based Medicine: Levels of Evidence (2009)


Research Designs in the Hierarchy

Clinical Questions --- Research Designs

Different types of clinical questions are best answered by different types of research studies.  You might not always find the highest level of evidence (i.e., systematic review or meta-analysis) to answer your question. When this happens, work your way down to the next highest level of evidence.

This table suggests study designs best suited to answer each type of clinical question.

Clinical Question

Suggested Research Design(s)

All Clinical Questions

Systematic review, meta-analysis


Randomized controlled trial (RCT), meta-analysis 
Also: cohort study, case-control study, case series


Randomized controlled trial (RCT), meta-analysis, cohort study 
Also: case-control study, case series


Randomized controlled trial (RCT) 
Also: cohort study


Randomized controlled trial (RCT), meta-analysis 
Also: prospective study, cohort study, case-control study, case series


Cohort study
Also: case-control study, case series


Qualitative study

Quality Improvement

Randomized controlled trial (RCT) 
Also: qualitative study 


Economic evaluation