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Evidence Based Medicine

This page provides information on locating and evaluating literature used to support evidence based practice.

Evidence Pyramid

Evidence Pyramid with Study Type Descriptions

These are some of the publication types that are associated with higher levels of evidence. You may want to start at the top of the pyramid and work your way down. However, remember that the pyramid is not the whole story. You should also consider the type of question you are asking.

Publication Types by Question Type: Different study types are suited to different questions. For example:

Most Clinical Questions: Systems, summaries, synopses, syntheses, meta-analyses, systematic reviews
Therapy: Randomized Controlled Trial
Diagnosis: Prospective, blind controlled trial compared to gold standard
Prognosis: Cohort study, case control, case series/case report

Study Designs

These are a few of the publication types associated with evidence-based practice taken from the Glossary of EBM Terms from the Centre for Evidence-Based Medicine Toronto, Accessing Preappraised Evidence: Fine Tuning the 5S Model into a 6S Model, and from the MeSH Database http://www.ncbi.nlm.nih.gov/mesh

Systems: An electronic medical record that is able to link updated, evidence-based information related to a patient's clinical information. Also known as an integrated computerized decision support system. Very few exist at this time.

Summary: These include topic summaries and clinical practice guidelines that integrate evidence-based information about specific clinical problems with regular updating.

Synopses of Syntheses: A synthesis would be a systematic review (defined below). A synopsis of that synthesis would be an expert/authoritative appraisal or critique of a high quality systematic review that provides sufficient information to support clinical action.

Syntheses: A summary of the medical literature that uses explicit methods to perform a comprehensive literature search and critical appraisal of individual studies. There are two categories of synthesis.

  • Systematic Reviews: A qualitative integration or description of individual studies.
  • Meta-analysis: A quantitative integration of data from individual studies using statistical techniques.

Synopses of Single Studies: An expert/authoritative appraisal or critique of an individual study that provides sufficient information to support clinical action.

Randomized Controlled Trial: A study in which participants are randomly allocated into an experimental group or control group and followed over time for the variables/outcomes of interest.

Cohort Studies: 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. A cohort study will have a control group that represents the unexposed population.

Case Controlled Studies: A study which involves identifying patients who have the outcome of interest (cases) and patients without the same outcome (controls), and looking back to see if they had the exposure of interest.

Case Series/Reports: A report on a series of patients or single patient with an outcome of interest. No control group is involved.

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