Levels of Evidence - Evidence Based Practice - LibGuides at Bloomsburg University of Pennsylvania Library

Evidence Pyramid for Studies

This pyramid illustrates the levels of evidence strength for different types of studies, found in databases like CINAHL and MEDLINE. Evidence strength decreases as you move down the pyramid, while at the same time the number of articles increases. As you can see, Systematic Reviews are at the top of this pyramid, because they provide the strongest evidence by pooling the evidence from many individual studies.

The Expanded Evidence Pyramid

This pyramid includes other sources for evidence, not all of which are available to you at BU, such as a Computerized Decision Support System. Generally speaking, those that are available for you to search are indicated by the green 'Search' bracket below.

As you look for the best evidence to answer a clinical question, a good rule of thumb is to begin your search as high up in the pyramid as you can. Summaries, Synopses, and Syntheses appraise the evidence in multiple studies so are especially good sources to locate relevant studies.

From EBM, Ruth Lilly Medical Library, Indiana University School of Medicine

Qualitative Research Pyramid

Further definition


LEVEL	DESCRIPTION	WHERE FOUND (EXAMPLES)
Systems	= Computerized Decision Support, electronic medical record that links patient problems to best evidence (relatively rare)	Workplace
Summaries	= Critically-Appraised Topics and Evidence-Based Guidelines	AHRQ National Guideline Clearinghouse
Synopses	= Critically-Appraised Journal Articles or SRs	Database of Abstracts of Reviews of Effects (DARE)
Syntheses	= Systematic Reviews	Cochrane Database of Systematic Reviews \| PubMed \| CINAHL \| PsycINFO
Studies	= RCTs, Cohort Studies, Case-Control Studies, Case Series/Reports	PubMed \| CINAHL \| PsycINFO
Expert Opinion	= Review Articles or Textbooks	PubMed \| CINAHL \| PsycINFO

Matching questions to studies

Even though you may not be able to find a systematic review on your question, nevertheless certain types of studies will provide good evidence, depending on the question. For example:

Most Common Type of Questions:	Preferred type of study:
Diagnosis How to select and interpret diagnostic tests	Comparison of new test to a 'gold standard' test
Effectiveness of Therapy How to select treatments that do more good than harm and that are worth the efforts and costs of using them	Randomized controlled trials Cohort studies
Prognosis How to estimate the patient’s likely clinical course over time based on factors other than the intervention and anticipate likely complications of disease	Cohort studies Case control studies
Harm/Etiology How to identify causes for disease, including iatrogenic forms	Cohort studies Case control studies
Meaning How to identify beliefs, perceptions, attitudes	Qualitative studies (multiple design)