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Levels of Evidence

The Research Pyramid

The gold standard of evidence is a systematic review:  an article which examines, appraises and consolidates findings of  all of the primary research for a medical question. 

In the middle section, Clinical research constitutes content that is vetted and verified such as clinically appraised topics and clinically appraised articles.  

The bottom level of information in medical practice is opinion and background information.  The kind of information that may be found in a textbook or encyclopedia.

Sources on the chart to the left give tips on how to retrieve specific levels of evidence from journal databases.

image of a pyramid showing the different levels of evidence. Systematic reviews are at the highest level, followed by clinically appraised evidence or articles, followed by randomized controlled trials, cohort studies.  The bottom level of information would be background information.

Dictionary of Evidence Based Medicine terms Center for Evidence Based Medicine

Searching for levels of evidence

Systematic Reviews

Health is a free index of systematic reviews from 1995 on in public health. Registration required.

Search the Database of Abstracts of Reviews (DARE) subset in the EBM/Cochrane Database 

PubMed Clinical Queries Search or conduct a search from the main screen and filter by article type

CINAHL (filter by publication type)

Clinically appraised topics

NGC National Guideline Clearinghouse

Evidence based clinical practice guidelines. (US) Updated weekly.

Clinically appraised individual articles

The ACP Journal Club  can be accessed in print.  It is also a subset of  the EBM/Cochrane Database.

Evidence Based Nursing  (print journal)

Searching Multiple Types of Filtered EBM Information

The TRIP Database

In CINAHL  you may filter by multiple publication types such as case study, clinical trial, randomized control trial, research, systematic review)

Randomized Controlled Trials

The  Cochrane Central Register of Controlled Trials is a subset of the EBM Cochrane database

PubMed – filter by article type after searching options for clinical trial, randomized control trial etc.

CINAHL – use the filter on the advanced search screen

Cohort Studies

There is no filer.  In PubMed add the MeSH  subject  Cohort Studies.  In CINAHL use the subject Prospective Studies

Case Controlled Studies/Case Series Reports

In CINAHL refer to the subject heading Case Controlled Studies

Background Information

For Encyclopedias and Reference sources see the Reference Sources section of this guide.  Northern Ontario School of Medicine may also be accessed.  See Instructions.

Comprehensive indexes to EBM

Best Practices, Guidelines, and Other EBM Sources

Best Practice Guidelines

Registered Nurses of Ontario Best Practice Guidelines

NICE Clinical Guidelines (National Institute for Health and Clinical Evidence, UK)

National Guidelines Clearinghouse (United States)

CMA Infobase - Canadian Medical Association  Canadian Clinical Practice Guidelines

Public Health Agency of Canada:  Best Practices Portal

Evidence Based Search Tools

BMJ Evidence Updates

Synopses of single studies

Evidence Based Nursing (Journal)