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Is All Evidence Created Equal?
The medical literature is immense, but only a small portion of it is
immediately useful in answering clinical questions. The literature
reports the whole spectrum of the scientific research process --
the long journey from in-vitro studies to double-blind randomized
controlled trials. This has been called the "wedge of
evidence" or the "pyramid of evidence."
An understanding of how various levels of evidence are reported and how
this literature is organized will help the searcher retrieve the
highest levels of
evidence for a particular clinical question. High levels of evidence may
not exist for all clinical questions because of the nature of medical
problems and research and ethical limitations.
Adding METHODOLOGY terms and CLINICAL FILTERS to
SUBJECT terms will
result in the most efficient and optimal retrieval in terms of finding
the highest level of evidence in answering clinical questions.
SUBJECT TERMS
plus
METHODOLOGICAL TERMS
equal
OPTIMAL RETRIEVAL of HIGH LEVELS of EVIDENCE
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Levels of Clinical Evidence in the Primary
Literature
Type of Question |
Type of
Study/Methodology |
MEDLINE Filters |
Therapy |
Double-Blind
Randomized Controlled
Trial |
Randomized Controlled Trial [PT],
double [TW] and
blind
[TW] |
Diagnosis |
Controlled Trial |
Sensitivity and Specificity [MH],
Diagnosis [SH] |
Prognosis |
Cohort Studies,
Case Control,
Case Series |
EXP Cohort Studies [MH],
Prognosis [MH],
Survival Analysis [MH] |
Etiology |
Cohort Studies |
EXP Cohort
Studies [MH],
Risk [TW] |
Prevention |
Randomized Controlled Trial,
Cohort
Studies |
Randomized Controlled Trial [pt],
Cohort Studies [MH],
Prevention and Control
[SH]
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Quality Improvement |
Randomized Controlled Trials |
Randomized Controlled Trial [PT]
Practice Guideline
[PT]
Consensus Development Conference [PT]
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For a visual "evidence pyramid," see SUNY Downstate
Medical Center EBM Course: A Guide to Research Methods.
The 4-S Hierarchy of Evidence (Studies,
Syntheses, Synopses, Systems) developed by R. Brian Haynes can be found
at http://ebm.bmjournals.com/cgi/content/full/6/2/36
For a more detailed discussion, see "Levels of Evidence and Grades of
Recommendations" at
http://www.cebm.net/levels_of_evidence.asp#levels
(Abbreviations: EXP=Explode; MH=Medical Subject Heading; PT=Publication
Type;
SH=Subheading; TI=Title; TW=Text Word)
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The
Secondary/Filtered/Synthesized Literature
Outcome Products of
Evidence Based Medicine
Filtered/Synthesized
Information |
Description/Definition |
How
To Find |
SYSTEMATIC
REVIEWS |
-differ
from
traditional review
articles in that conclusions are evidence-based rather than
commentary
-start with a clearly articulated question -use explicit,
rigorous methods to identify, critically appraise, and synthesize relevant
studies
-appraise relevant published and unpublished evidence before
combining and analyzing data -include description of how primary data
sources are identified -individual studies assessed for
validity
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*Cochrane
Collaboration
-Cochrane Database of Systematic Reviews
-
York Database of
Abstracts of
Reviews of Effectiveness
- Cochrane Controlled
Trials Register
-Cochrane Review Methodology Database
*In
MEDLINE:
-Review [pt] AND medline [tw]
-(Quantitative OR Systematic
OR Methodologic)
AND (Review OR
Overview)
*In PubMed Clinical Queries "Systematic Review" is
available as a limit option.
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META-ANALYSES |
-a specific
methodologic and
statistical technique for combining quantitative data
-a type of
systematic overview
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*Cochrane Databases
*In
MEDLINE:
-Meta-analysis [pt]
-meta-anal* [tw] OR
-metaanal*
[tw]
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EVIDENCE-BASED
PRACTICE
GUIDELINES |
-gather,
appraise, combine evidence systematically
-statements designed to
assist
practitioner and patient decisions
-developed by professional
groups,
government agencies, local practices
-structured abstract:
objective, option, outcomes, evidence, values,
benefits/harms/costs, recommendation, validation, sponsors
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*National Guidelines Clearinghouse
http://www.guideline.gov
*Agency for Healthcare Research and Quality
http://www.ahrq.gov/
*US Preventive Services Task Force Recommendations
http://www.ahrq.gov/clinic/cps3dix.htm
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CRITICALLY
APPRAISED
TOPICS (CATs) |
-literature scanned for clinically relevant studies -critically
appraise
the studies
-provide commentary on strength of study and clinical
significance
-one-page format
-CATmaker software from CEBM
http://www.cebm.net/catmaker.asp
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*EBM
Reviews -- ACP Journal Club (UIC
access via the Library List of Electronic Resources)
*InfoPOEMS -- Essential EvidencePLUS (access via the Library List of Electronic
Resources)
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DECISION
ANALYSES |
-studies that analyze
decisions faced by
clinicians for an individual patient, about clinical policy, or a global
health care policy
-application of explicit, quantitative methods to
analyze decisions under conditions of uncertainty
-makes fully
explicit
all the risks and benefits of a decision -include a decision
tree
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*In MEDLINE:
Decision Support Techniques
[MH]
Cost-Benefit Analysis [MH]
decision analysis [TI]
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This page is maintained at
www.uic.edu/depts/lib/lhsp/resources/ebm.shtml
by Jo
Dorsch, UIC
Library of the Health Sciences-Peoria. Please send comments to Jo Dorsch
jod@uic.edu.
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Last updated: Friday, 07-Mar-2008 14:46:31 CST
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