Glossary

Welcome to the CEBM Glossary. This is not a comprehensive glossary but it outlines some of the key terms that should be understood in relation to Evidence-Based practice.

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Absolute risk reduction (ARR): The difference in the event rate between control group (CER) and treated group (EER): ARR = CER - EER.

Bias: Any tendency to influence the results of a trial (or their interpretation) other than the experimental intervention.

Blinding: A technique used in research to eliminate bias by hiding the intervention from the patient, clinician, and/or other researchers who are interpreting results.

Case""control study: Involves identifying patients who have the outcome of interest (cases) and control patients without the same outcome, and looking to see if they had the exposure of interest.

Case-series: A report on a series of patients with an outcome of interest. No control group is involved.

CER: Control event rate; see event rate.

Clinical practice guideline: A systematically developed statement designed to assist health care professionals and patients make decisions about appropriate health care for specific clinical circumstances.

Cochrane collaboration: A worldwide association of groups who create and maintain systematic reviews of the literature for specific topic areas.

Cohort study: Involves the identification of two groups (cohorts) of patients, one which did receive the exposure of interest, and one which did not, and following these cohorts forward for the outcome of interest.

Confidence interval (CI): The range around a study's result within which we would expect the true value to lie. CIs account for the sampling error between the study population and the wider population the study is supposed to represent. See p11

Confounding variable: A variable which is not the one you are interested in but which may affect the results of trial.

Critically appraised topic (CAT): A short summary of an article from the literature, created to answer a specific clinical question.

Decision analysis: The application of explicit, quantitative methods to analyse decisions under conditions of uncertainty.

EER: Experimental event rate; see Event rate.

Effectiveness: A measure of the benefit resulting from an intervention for a given health problem under usual conditions of clinical care for a particular group.

Efficacy: A measure of the benefit resulting from an intervention for a given health problem under the ideal conditions of an investigation.

Event rate: The proportion of patients in a group in whom an event is observed..

Forrest plot: A diagrammatic representation of the results of individual trials in a meta-analysis.

Funnel plot: A method of graphing the results of trials in a meta-analysis to show if the results have been affected by publication bias.

Heterogeneity: In systematic reviews, the amount of incompatibility between trials included in the review, whether clinical (ie the studies are clinically different) or statistical (ie the results are different from one another).

Incidence: The number of new cases of illness commencing, or of persons falling ill, during a specified time period in a given population.

Intention-to-treat: Characteristic of a study where patients are analysed in the groups to which they were originally assigned, even though they may have switched treatment arms during the study for clinical reasons.

Likelihood ratio: The likelihood that a given test result would be expected in a patient with the target disorder compared to the likelihood that the same result would be expected in a patient without that disorder.

for a positive test result = LR+ = sensitivity/(1-specificity)
for a negative test result = LR- = (1-sensitivity)/specificity

MeSH: Medical Subject Headings: a thesaurus of medical terms used by many databases and libraries to index and classify medical information.

Meta-analysis: A systematic review which uses quantitative methods to summarise the results.

Negative predictive value (-PV): The proportion of people with a negative test who are free of disease.

Number needed to treat (NNT): The number of patients who need to be treated to prevent one bad outcome. It is the inverse of the ARR: NNT=1/ARR. Numbers needed to harm (NNH)-the number of patients who, if they received the experimental treatment, would lead to one additional person being harmed compared with patients who receive the control treatment; calculated as 1/ARI.

Odds: A ratio of events to non-events. If the event rate for a disease is 0.2 (10%), its non-event rate is 0.8 and therefore its odds are 2/8.

p value: The probability that a particular result would have happened by chance.

Positive predictive value (+PV): The proportion of people with a positive test who have disease.

Post-test probability: The probability that a patient has the disorder of interest after the test result is known.

Pre-test probability: The probability that a patient has the disorder of interest prior to administering a test.

Prevalence: The baseline risk of a disorder in the population of interest.

Publication bias: A bias in a systematic review caused by incompleteness of the search, such as omitting non-English language sources, or unpublished trials (inconclusive trials are less likely to be published than conclusive ones, but are not necessarily less valid).

Randomised controlled clinical trial: A group of patients is randomised into an experimental group and a control group. These groups are followed up for the variables/outcomes of interest.

Relative risk (RR) (or risk ratio): The ratio of the risk of an event in the experimental group compared to that of the control group (RR=EER / CER). Not to be confused with relative risk reduction (see below).

Relative risk reduction (RRR): The percentage reduction in events in the treated group event rate (EER) compared to the control group event rate (CER): RRR = (CER-EER) / CER.

Sensitivity: The proportion of people with disease who have a positive test.

Specificity: The proportion of people free of a disease who have a negative test.

Systematic review: An article in which the authors have systematically searched for, appraised, and summarised all of the medical literature for a specific topic.

Validity: The extent to which a variable or intervention measures what it is supposed to measure or accomplishes what it is supposed to accomplish. The internal validity of a study refers to the integrity of the experimental design. The external validity of a study refers to the appropriateness by which its results can be applied to non-study patients or populations.

Page last edited: 05 July 2010

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