The Brookbush Institute Publishes a NEW Glossary Term: 'Levels of Evidence'

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NEW YORK, NY, UNITED STATES, August 15, 2025 /EINPresswire.com/ -- - Excerpt from Glossary Term: Levels of Evidence
- Additional Glossary Term: Evidence-based Practice
- Related Article: Meta-analysis Problems: Why do so many imply that nothing works?


DEFINITION
Levels of evidence are proposed hierarchies of research types that intend to rank the strength and reliability of research findings based on study design. However, the idea that research can be ranked based on study design alone is controversial. In evidence-based practice , levels of evidence hierarchies were developed to help clinicians and researchers quickly assess the relative confidence they can place in study results when making clinical decisions. However, these levels should be viewed as guidelines rather than absolutes, as they do not replace the need for critical appraisal of study quality, methodology, or relevance to the patient population in question.

COMMON LEVELS OF EVIDENCE HIERARCHIES
Several organizations and methodologists have proposed evidence hierarchies to help clinicians and researchers estimate the relative trustworthiness of research designs. These hierarchies typically rank study types based on their ability to minimize bias and control confounding variables.

Among the most frequently cited frameworks are:
- Oxford Centre for Evidence-Based Medicine (OCEBM)
- GRADE (Grading of Recommendations, Assessment, Development, and Evaluations)
- U.S. Preventive Services Task Force
- Shekelle et al. (1999) Levels of Evidence

Shekelle et al. (1999) Hierarchy (often cited):
- IA – Evidence from meta-analysis of randomized controlled trials
- IB – Evidence from at least one randomized controlled trial
- IIA – Evidence from at least one controlled study without randomization
- IIB – Evidence from at least one other type of quasi-experimental study
- III – Evidence from non-experimental descriptive studies, such as comparative studies, correlation studies, or case-control studies
- IV – Evidence from expert committee reports, opinions, or respected clinical experience
(Shekelle, P. G., Woolf, S. H., Eccles, M., & Grimshaw, J., 1999)

FREQUENTLY ASKED QUESTIONS
What is level II evidence?
- Although many different hierarchies exist, this typically refers to randomized controlled trials (RCTs).

What is level III evidence?
- Although many different hierarchies exist, this typically refers to observational research.

What is level IV, V, VI, and VII research?
- Because the various levels of evidence hierarchies are not identical and become increasingly divergent with each level, it is not possible to say for sure without knowing which hierarchy is being referred to.

What is the purpose of levels of evidence?...

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Brent Brookbush
Brookbush Institute
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