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What types
of studies or data will be most helpful in answering your
question?
Medical literature is
immense, but only a small portion is immediately useful in answering clinical
questions. The literature reports the whole spectrum of the scientific research
process from in-vitro studies to double-blind randomized control trials. This
spectrum is called the “wedge of evidence” or the “pyramid of
evidence.”
TRIP (Turning Research Into
Practice)
Trip is a clinical search
engine designed to allow users to quickly and easily find and use high-quality
research evidence to support their practice and/or care. As well as research
evidence, TRIP allows clinicians to search across other content types including
images, videos, patient information leaflets, educational courses and
news.
| Definitions of Types of Studies
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Meta-analysis
Following a systematic review, data from individual
studies may be pooled quantitatively and reanalysed using established
statistical methods. This technique is called meta-analysis. A meta-analysis
will thoroughly examine a number of valid studies on a topic and combine the
results using accepted statistical methodology as if they were from one large
study. Some clinicians put meta-analysis at the top of the pyramid because part
of the methodology includes critical appraisal of the selected RCTs for
analysis. PubMed's Clinical Queries is a good place to
start.
Systematic Reviews
Systematic reviews usually focus on a clinical topic and
answer a specific question. An extensive literature search is conducted to
identify all studies with sound methodology. The studies are reviewed,
assessed, and the results are summarized according to the predetermined
criteria of the review question. The Cochrane Collaboration has done a
lot of work in the area of systematic review.
Evidence
Syntheses
Authors of critically-appraised topics evaluate and
synthesize multiple research studies, so that practitioners may more readily
determine if the evidence is valid and reliable, and whether they can apply it
to their own practice. Dynamed is an example of a resource that contains
evidence syntheses.
Article
synopses
Authors of critically-appraised individual articles
evaluate and synopsize individual research studies so that practitioners may
more readily determine if the evidence is valid and reliable, and whether they
can apply it to their own practice. The ACP Journal Club is an example
of a resource that contains article synopses.
Randomized Controlled Trials
Randomized controlled trials are carefully planned
projects that study the effect of a therapy on real patients. They include
methodologies that reduce the potential for bias (randomizing and blinding) and
that allow for comparison between intervention groups and control groups (no
intervention). PubMed's Clinical Queries is a
resource.
A double blind
study is one in which neither the patient nor the physician knows whether the
patient is receiving the treatment of interest or the control
treatment.
Crossover Design
A controlled trial where each study participant has
both therapies, e.g, is randomised to treatment A first, at the crossover point
they then start treatment B. Only relevant if the outcome is reversible with
time, e.g, symptoms. Subjects act as own control.
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Cohort
Studies
Cohort Studies take a large population and follow
patients who have a specific condition or receive a particular treatment over
time and compare them with another group that has not been affected by the
condition or treatment being studied. Cohort studies are observational and not
as reliable as randomized controlled studies, since the two groups differ in
ways other than in the variable under study. PubMed's Clinical Queries
is a good resource.
Case
Controlled Studies
Case controlled studies are studies in which patients
who already have a specific condition are compared with people who do not. They
often rely on medical reports and patient recall for data collection. These
types of studes are often less reliable than randomized controlled trials and
cohort studies because showing a statistical relationship does not mean that
one factor necessarily caused the other. PubMed's Clinical Queries is a
good resource.
Cross-Sectional Study
A study that examines the relationship between diseases
(or other health-related characteristics) and other variables of interest as
they exist in a defined population at one particular time (ie exposure and
outcomes are both measured at the same time). Best for quantifying the
prevalence of a disease or risk factor, and for quantifying the accuracy of a
diagnostic test.
Difference Between Cohort, Case-Controlled, and Cross-Sectional
Studies -- Time is the Key
The Cohort (Prospective) design measures exposure in
the present and the disease in the future.
The Case-Control (Retrospective)
design measures the disease in the present and looks backwards for exposure
history.
The simplest is the Cross-Sectional (Prevalence) design which is
conducted completely at present.
Case
Series/Case Reports
Case series and case reports consist of collections of
reports on the treatment of individual patients or a report on a single
patient. Because they are reports of cases and use no control groups with which
to compare outcomes, they have no statistical validity.
Background Information/Expert Opinion
Evidence in these resources may vary from expert opinion
to high levels of evidence. |
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Levels
of Evidence
Evidence-based
medicine involves tracking down the available evidence, assessing its validity
and then using the “best” evidence to inform decisions regarding
care. Rules of evidence have been established to grade evidence according to
its strength. The terms "levels of evidence" or "strength of evidence" refer to
systems for classifying the evidence in a body of literature through a
hierarchy of scientific rigor and quality. Several dozen of these hierarchies
exist. Some systems comprise three levels and others eight or more.
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Where will
you search?
Filtered Resources
Filtered resources appraise the quality of
studies and often make recommendations for practice.
Systematic Reviews /
Meta-Analyses
Authors of a systematic
review ask a specific clinical question, perform a comprehensive literature
search, eliminate the poorly done studies and attempt to make practice
recommendations based on the well-done studies. A meta-analysis is a
systematic review that combines all the results of all the studies into a
single statistical analysis of results.
Cochrane This resource is a regularly updated collection of
evidence-based medicine databases. It includes abstracts and full reviews of
controlled trials, methodologies, economic evaluation, and health technology
assessment. Many consider the Cochrane Database of Systematic Reviews to be the
“gold standard” of systematic reviews.
Systematic Reviews and Meta-Analyses are also
searchable in MEDLINE:
- PubMed Select "Clinical
Queries" or perform a search and then select "Meta-Analysis" and/or "Systematic
Reviews" from the list of "Article Types."
- Embase Select "Cochrane
Review", "Systematic Review" and/or "Meta Analysis"
- PICO searching from NLM
is a specialty interface where Patient/Problem, Intervention, Compare to, and
Outcome factors are entered to search MEDLINE. Choose "Meta-Analysis" from the
"Select Publication Type" pull-down menu. Not geting any results? Don't select
any publication type.
- Already
have your PICO Question formulated, use
askMEDLINE, a
free-text, natural language search tool for MEDLINE/PubMed.
Critically-Appraised Topics
Authors of critically-appraised
topics evaluate and synthesize multiple research studies.
DynaMedex
Combines the
clinical expertise and curated disease content of DynaMed with the
comprehensive drug information of Micromedex. This integration allows faculty,
staff and learners to access evidence-based recommendations and drug dosing,
interaction, and IV compatibility information in one tool.
Critically-Appraised Individual
Articles
Authors of critically-appraised
individual articles evaluate and synopsize individual research
studies.
The ACP Journal
Club
The editors
of this journal screen the top 100+ clinical journals and identify studies that
are methodologically sound and clinically relevant. An enhanced abstract, with
conclusions clearly stated, and a commentary are provided for each selected
article. Published by the American College of Physicians-American Society of
Internal Medicine.
Unfiltered Resources
Evidence is not always available via filtered resources.
Searching the primary literature may be required. It is possible to use
specific search strategies in PubMed and other databases to achieve the highest
possible level of evidence.
Discovery
Discovery is
an online tool that "pulls together" almost all of the resources of our
Libraries so that they can be explored using a single search box. Think of
Search Everything as the MUSM Libraries' version of Google.
PubMed
To limit your
PubMed search to the best evidence-producing studies: Click on "clinical
queries" (on the left side of the screen). This specialized search is intended
for clinicians and has built-in search "filters." Four study
categories--therapy, diagnosis, etiology, prognosis--are provided, and you may
indicate whether you wish your search to be more sensitive (i.e., include most
relevant articles but probably including some less relevant ones) or more
specific (i.e., including mostly relevant articles but probably omit a
few).
Clinical
Key
Provides
access to 900+ books, 500+ journals, the First Consult point of care database,
over 1 million images, and 3,000+ videos from Procedures Consult..
PsycINFO
International
coverage of the professional and academic literature in psychology, medicine,
psychiatry, nursing, sociology, education, pharmacology, physiology,
linguistics, and other areas.
To limit your
PsycINFO search to the best evidence-producing studies: Click on the "Limits"
icon to use "Clinical Queries" or limit to "methodology" types.
Background Information/Expert
Opinion
Note:
Evidence in these resources may vary from expert opinion to high levels of
evidence.
Medscape
Has over
10,000 physician authors and editors who create thousands of peer-reviewed,
disease specific articles. Includes over 100 useful medical tools and
calculators, as well as a clinical image case, radiograph and ECG of the week,
and over 30,000 images.
Access is
free.
eBooks
Access over
17,000 electronic textbooks.
AccessMedicine
It has over
90 electronic textbooks and reference books including: Harrison's Principles of
Internal Medicine; Hurst’s the Heart; Metabolic and Molecular Bases of
Inherited Diseases; the Lange series in the basic medical and clinical
sciences; and color atlases of cardiology, dermatology, microbiology,
hematology, endoscopy and others.
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