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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." (for a visual representation see More Information)
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.
Studies can be descriptive (or observational), such as:
Case Reports [MeSH Publication Type] - "Clinical presentations that may be followed by evaluative studies that eventually lead to a diagnosis."
Case Series - Descriptions of groups of patients with a disease.
Case-Control Studies [MeSH Term] - "Comparisons that start with the identification of persons with the disease or outcome of interest and a control (comparison, referent) group without the disease or outcome of interest. The relationship of an attribute is examined by comparing both groups with regard to the frequency or levels of outcome over time."
Cohort Studies [MeSH Term] - "Studies in which subsets of a defined population are identified. These groups may or may not be exposed to factors hypothesized to influence the probability of the occurrence of a particular disease or other outcome. Cohorts are defined populations which, as a whole, are followed in an attempt to determine distinguishing subgroup characteristics."
Or evaluative (interventional), such as a:
Randomized Controlled Trial [MeSH Publication Type] - "A work that reports on a clinical trial that involves at least one test treatment and one control treatment, concurrent enrollment and follow-up of the test- and control-treated groups, and in which the treatments to be administered are selected by a random process, such as the use of a random-numbers table."
Studies can also be time-based:
Type of Question |
Type of Study Methodology |
MEDLINE Filters |
---|---|---|
Therapy: information needed about |
Double-Blind |
Randomized Controlled Trial [PT] |
Diagnosis: information needed about a |
Controlled Clinical Trial |
Sensitivity and Specificity [MH] |
Prognosis: information needed about the |
Cohort Studies |
Cohort Studies [MH] Prognosis [MH] Survival Analysis [MH] |
Etiology/Harm: information needed about |
Cohort Studies |
Cohort Studies [MH] |
Prevention: information needed about the |
Randomized Controlled Trial |
Randomized Controlled Trial [PT] Cohort Studies [MH] Prevention and Control [SH] |
Quality Improvement: information needed |
Randomized Controlled Trial |
Randomized Controlled Trial [PT] |
(Abbreviations: MH=Medical Subject Heading; PT=Publication Type; SH=Subheading; TW=Text Word)
The practice and teaching of Evidence Based Medicine has outcome products which help the health care provider and consumer keep up with the medical literature and assess the evidence. This secondary literature synthesizes, filters, and evaluates the primary research literature. Dissemination and incorporation of valid clinical research findings into medical practice is the ultimate goal.
There are several types of secondary literature:
There are also several products, or tools, that synthesize the literature. To learn more about these, visit the PRE-APPRAISED SUMMARIES page.
Systematic Reviews are NOT the same as traditional reviews. Systematic Reviews start with a clearly articulated question and use explicit and rigorous methods. They include a description of how primary data sources and articles are found and selected for inclusion. They critically appraise the found evidence by assessing their validity, reliability, and other measures of quality. Finally, Systematic Reviews combine and analyze the results of this evidence to synthesize it into an evidence based review.
Sources of Systematic Reviews include:
When searching PubMed try the
Or adding one of these to your search
Meta-analyses are similar to Systematic Reviews, but they include a specific methodologic and statistical technique for combining quantitative data. They provide an evidence based overview of multiple studies with combined quantitative analysis.
Sources of Meta-analyses include:
When searching PubMed try the
Or adding one of these to your search
Evidence Based Practice Guidelines gather, appraise, and combine evidence systematically. They are typically developed by professional groups, government agencies, or expert panels. They include statements designed to assist practitioner and patient decisions. Not all practice guidelines are evidence based so look for critical information about the methodology used or about the group that produced the guideline.
Sources of Evidence Based Practice Guidelines include:
Critically Appraised Topics (CATs) scan the literature for clinically relevant studies and critically appraise them. CATs provide commentary on the strength of the study and its clinical significance in a short, one-page format. Find out more on the APPRAISAL page.
Sources of Critically Appraised Topics (CATs) include:
Decision Analyses or Decision Tools are studies that analyze decisions faced by clinicians for an individual patient, about clinical policy, or about global health care policy. They include the application of explicit, quantitative methods to analyze decisions under conditions of uncertainty. Risks and benefits of a decision are made fully explicit and a decision tree is usually included.
Sources of Decision Analyses or Decision Tools include:
When searching PubMed try adding one of these to your search
Consensus Development Reports are assessments of emerging or critical health issues, based on available research and expert opinion, to identify needs for policy development and further research. This definition is based on information from the NIH Consensus Development Program, which has now 'retired'.)
Similarly, "Consensus Development Conference" is a MeSH Publication Type meaning "a work that consists of summary statements representing the majority and current agreement of physicians, scientists, and other professionals meeting to reach a consensus on a selected subject."
Sources of Consensus Development Reports include:
When searching PubMed try the
Or adding this to your search
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