In research, the levels of evidence, also referred to as the hierarchy of evidence, refers to the differing levels of credibility and the strength of a study. Levels of evidence are assigned to clinical research studies based on the methodological quality of their design, validity, and applicability to patient care.3
The levels are usually ordered in quality from highest to lowest.
The systematic review or meta-analysis of randomized controlled trials (RCTs) and evidence-based practice guidelines are considered to be the strongest level of evidence on which to guide practice decisions. (Melnyk, 2004) The weakest level of evidence is the opinion from the authorities and/or reports of expert committees.
LibGuides: Evidence-Based Practice for Health Professionals: Levels of Evidence. Libguides.nvcc.edu. https://libguides.nvcc.edu/evidence-based-practice/levelsofevidence. Published 2022. Accessed July 15, 2022.
It is important to note that all levels of evidence are important and have their own value.
Typically, it will depend on your research question, which determines your type of research study, which will further clarify into which level of evidence your study falls. Additionally, organizations and journals have adopted variations in the levels of evidence to accommodate their differing specialties.1
In addition to ranking your own research studies, it is important to know the five levels of evidence when you are turning to the literature for further research, background, or practice.
In the medical and health care area, for example, it is very important that professionals not only have access to information but also have instruments to determine which evidence is stronger and more trustworthy, building up the confidence to diagnose and treat their patients.
Levels of evidence in research. Elsevier Author Services Scientific Publishing. https://scientific-publishing.webshop.elsevier.com/research-process/levels-of-evidence-in-research/. Published 2022.
- Burns PB, Rohrich RJ, Chung KC. The levels of evidence and their role in evidence-based medicine. Plast Reconstr Surg. 2011;128(1):305-310. doi:10.1097/PRS.0b013e318219c171
- Levels of evidence in research. Elsevier Author Services Scientific Publishing. https://scientific-publishing.webshop.elsevier.com/research-process/levels-of-evidence-in-research/. Published 2022.
- LibGuides: Evidence-Based Practice for Health Professionals: Levels of Evidence. Libguides.nvcc.edu. https://libguides.nvcc.edu/evidence-based-practice/levelsofevidence. Updated 2022.