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Evidence Based Medicine

This guide is designed to assist health care professionals and students become effective and efficient users of the medical literature.

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EBM Pyramid

Glossary of EBM Terms and Concepts


Bias - Prejudice or the lack of neutrality.  A systematic deviation from the truth that affects the conclusions and occurs in the process or design of the research. 

Blinding - Process by which the participants and/or some of the researchers do not know the groups to which the participants have been assigned. 

Case Control Studies [MeSH]* - Studies which start with the identification of persons with a disease of interest and a control (comparison, referent) group without the disease. The relationship of an attribute to the disease is examined by comparing diseased and non-diseased persons with regard to the frequency or levels of the attribute in each group.

Clinical Filters - A method for improving the retrieval of high quality studies applicable to clinical practice is to include search terms that select studies at advanced stages of testing for clinical application. Including one, or a combination of these terms, in a MEDLINE search strategy will selectively retrieve evidence-based literature that is more likely to answer clinical questions. 

Clinical Trial [MeSH Publication Type]* - Work that is the report of a pre-planned clinical study of the safety, efficacy, or optimum dosage schedule of one or more diagnostic, therapeutic, or prophylactic drugs, devices, or techniques in humans selected according to predetermined criteria of eligibility and observed for predefined evidence of favorable and unfavorable effects. While most clinical trials concern humans, this publication type may be used for clinical veterinary articles meeting the requisites for humans. Specific headings for specific types and phases of clinical trials are also available.

Confounding -A mixing of the effects within an experiment because the variables have not been sufficiently separated.  Possible confounding variables should be discussed in the report of the research.

Cohort Studies [MeSH]* - 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.

Consensus Development Conference [MeSH Publication Type]* - 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.

Control Group - The group that does not receive the treatment, etc.

Controlled Clinical Trial [MeSH Publication Type]* - Work consisting of a clinical trial involving one or more test treatments, at least one control treatment, specified outcome measures for evaluating the studied intervention, and a bias-free method for assigning patients to the test treatment. The treatment may be drugs, devices, or procedures studied for diagnostic, therapeutic, or prophylactic effectiveness. Control measures include placebos, active medicine, no-treatment, dosage forms and regimens, historical comparisons, etc. When randomization using mathematical techniques, such as the use of a random numbers table, is employed to assign patients to test or control treatments, the trial is characterized as a RANDOMIZED CONTROLLED TRIAL.

Critically Appraised Topics (CATs) - A CAT is a short summary of the evidence to a focused clinical question.  It allows users to store the results of their critical appraisal in such a way that they can easily be shared or stored for later use. 

Decision Analysis - The application of explicit, quantitative methods that quantify prognoses, treatment effects, and patient values in order to analyze a decision under conditions of uncertainty.

Dependent variable - The component of an experiment that changes, or not, as a result of the independent variable (for example - the existence of a disease). 

Follow-up Studies [MeSH]* - Studies in which individuals or populations are followed to assess the outcome of exposures, procedures, or effects of a characteristic, e.g., occurrence of disease.

Hypothesis - A statement that is believed to be true but has not yet been tested.

Independent variable - The component of an experiment that is controlled by the researcher (for example - a new therapy).

Longitudinal Studies [MeSH]* - Studies in which variables relating to an individual or group of individuals are assessed over a period of time.

Loss to Follow-up/Intention to Treat - Research design concept that not all of the participants will complete the research study but that they should be accounted for even though they did not fully participate.

Meta-Analysis [MeSH Publication Type]* - Works consisting of studies using a quantitative method of combining the results of independent studies (usually drawn from the published literature) and synthesizing summaries and conclusions which may be used to evaluate therapeutic effectiveness, plan new studies, etc. It is often an overview of clinical trials. It is usually called a meta-analysis by the author or sponsoring body and should be differentiated from reviews of literature.

P Value - The probability of any observed differences having happened by chance.  The convention is that .05 is required.    

Power - The liklihood that a study will detect a statistically significant difference.  The convention is that a power of at least 80% is required.

Practice Guideline [MeSh Publication Type]* - Work consisting of a set of directions or principles to assist the health care practitioner with patient care decisions about appropriate diagnostic, therapeutic, or other clinical procedures for specific clinical circumstances. Practice guidelines may be developed by government agencies at any level, institutions, organizations such as professional societies or governing boards, or by the convening of expert panels. They can provide a foundation for assessing and evaluating the quality and effectiveness of health care in terms of measuring improved health, reduction of variation in services or procedures performed, and reduction of variation in outcomes of health care delivered.

Randomization - Process that assigns participants by chance to either the treatment group or the control group.

Randomized Controlled Trial [MeSH Publication Type]* - Work consisting of 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.

Systematic review - A summary of the medical literature that uses explicit methods to perform a comprehensive literature search and critical appraisal of individual studies, and that uses appropriate statistical techniques to combine these valid studies.


*National Library of Medicine's Medical Subject Heading (MeSH) definition

†Straus, Sharon E.,  Evidence Based Medicine: How to practice and teach EBM. 3rd Ed. Elsevier Churchill Linvingstone.  2005.

‡Badenoch, D. and Heneghan, C.  Evidence-based Medicine Toolkit. BMJ Books. 2002.

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