The Evidence Hierarchy: What is best evidence?
Evidence hierarchies rank studies based upon the rigor (validity and reliability) of their research methods. The more rigorous the methodology the less risk of bias, which leads to the highest quality of evidence.
Study designs at the top of the evidence pyramid are considered to have more rigorous methodologies and are more likely to minimize the effect of bias on the results of the study.
"Evidence Pyramid" by Dartmouth Biomedical Libraries is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
Synthesized evidence, also known as filtered, presents evidence from multiple studies, which has been critically appraised by experts for its rigor (validity and reliability). This type of evidence is appropriate for clinical point-of-care decision-making. Sources of synthesized evidence can be found within systematic reviews, meta analyses and evidence-based clinical practice guidelines.
Benefits of synthesized research:
Limitations of synthesized research:
Examples of synthesized evidence:
What is the best evidence and how to find it. BMJ Best Practice. (n.d.). Retrieved September 16, 2021, from https://bestpractice.bmj.com/info/us/toolkit/discuss-ebm/what-is-the-best-evidence-and-how-to-find-it/.
Primary evidence, also know as unfiltered, are original single studies. This type of evidence has not been synthesized or aggregated with similar study results. Examples include Randomized Control Trials (RCTs), Cohort studies, Clinical trials, and Case-control.
Benefits of primary evidence:
Limitations of primary evidence:
Examples of Primary evidence:
|Question Domain||Description||Evidence Level|
|Therapeutic/Treatment||Effectiveness of intervention: treatment, medication, surgical procedure, exercise, lifestyle change||Randomized Control Trial (RCT)|
|Prevention||Effectiveness of an intervention or exposure to prevent mortality. Assessment of preventative measures and evaluation of potential harms/benefits||RCT or Prospective Study|
|Diagnosis||Measures the ability of a test or procedure to differentiate between diagnostic capabilities||RCT or Cohort Study|
|Prognosis||Measures the ability to forecast a probable cause of disease or illness development||Cohort Study or Case-Control Series|
|Etiology||Measures the harmful effects or an intervention or exposure||Cohort Study|
|Meaning||Documents patients' experiences or concerns||Qualitative Study|
Synthesized resources: Meta-Search Engines:
Meta search engines simultaneously search multiple evidence-based resources
Synthesized evidence: Systematic Reviews and Meta-Analyses:
Synthesized evidence: Critically-appraised topics (Evidence synthesis & Guidelines)
Authors of critically-appraised topics evaluate and synthesize multiple research studies
To access specific types of studies within these databases, use the built-in search filters.