These sources provide clinical guidelines, clinical summaries, synopses, health technology assessments, and other forms of highly processed synthesis of evidence to inform clinical recommendations. They take a step beyond a systematic review to offer recommendations for clinical practice.
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These sources offer select systematic reviews, synopses, and other integrations of primary study research from multiple sources into cohesive review articles.
These sources offer primary research studies.
Efficient EBD searches start at the level of evidence with the highest level of “processing” available before moving down.
Individual primary research studies are processed via specific, structured methods into systematic reviews, which in turn are integrated with clinical expertise and review to become clinical guidelines. Clinical guidelines and summaries from trustworthy creators are the most efficient starting point for an EBD search.
This chart from JADA shows the hierarchy of evidence for single primary studies mapped to the level of processing to the types of appropriate EBD resources to search.
Hierarchy of Evidence for Research Studies
Preappraised and nonpreappraised research studies are research, and also have a hierarchy of evidence. It is based on degree of assumed bias, based upon the evidence-based practice definition - "systematic deviation of study results from the ‘true’ results/effects on patients, because of the way(s) in which the study is conducted" (source)
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Pre-Appraised Research
Non Pre-Appraised Research
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Meta-Analysis Systematic Review Randomized Control Trial (RCT) Cohort Study Case Control Study Case Series/Case Report Animal Research/Laboratory Study
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For more detailed information about the levels of evidence see the Oxford Centre for Evidence-based Medicine - Levels of Evidence (March 2009). Drawn from the UNC Chapel Hill Evidence-Based Dentistry Guide.
Definitions of Study Types, in hierarchical order
(From BMJ’s Glossary of EBM terms)
| Meta-analysis |
A statistical technique that summarizes the results of several studies in a single weighted estimate, in which more weight is given to results of studies with more events and sometimes to studies of higher quality. |
| Systematic Review |
A review in which specified and appropriate methods have been used to identify, appraise, and summarize studies addressing a defined question. I
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| Randomized Controlled Trial |
Experimental study in which participants are randomly assigned to two or more groups: at least one (the experimental group) receiving an intervention that is being tested and another (the comparison or control group) receiving an alternative treatment or placebo.
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| Controlled Clinical Trial |
Experimental study in which participants are assigned to two or more different treatment groups, typically by a method other than random allocation.
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| Cohort Study |
Observational study design that follows a group of people (a cohort), and then looks at how events differ among people within the group.
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| Case control study |
Observational study comparing a group of people who have experienced a specific event (usually an adverse event) and a group of people who have not experienced the same event, and looks at how exposure to suspect (usually noxious) agents differed between the two groups.
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| Case Series |
Observational analysis of a series of people with the disease (there is no comparison group in case series).
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