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Glossary of Terms

The following glossary, adapted from the Centre for Evidence Based Medicine, Oxford


  • Absolute Risk Reduction (ARR)is the difference in the event rate between control group (CER) and treated group (EER): ARR = CER - EER.


  • Blinded A study is blinded if any or all of the clinicians, patients, participants, outcome assessors, or statisticians were unaware of who received which study intervention. The double double-blind usually refers to patient and clinician being blind, but is ambiguous so it is better to state who is blinded.


  • Case-control Study involves identifying patients who have the outcome of interest (cases) and control patients without the same outcome, and looking back to see if they had the exposure of interest. 


  • Case-series is 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 is a systematically developed statement designed to assist practitioner and patient make decisions about appropriate health care for specific clinical circumstances.


  • Cohort Study involves 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 CI quantifies the uncertainty in measurement; usually reported as 95% CI, which is the range of values within which we can be 95% sure that the true value for the whole population lies.


  • Cost-Benefit Analysis converts effects into the same monetary terms as the costs and compares them.


  • Cost-Effectiveness Analysis converts effects into health terms and describes the costs for some additional health gain (e.g. cost per additional MI prevented).


  • Cost-Utility Analysis converts effects into personal preferences (or utilities) and describes how much it costs for some additional quality gain (e.g. cost per additional quality-adjusted life-year, or QALY).


  • Crossover Study Design: the administration of two or more experimental therapies one after the other in a specified or random order to the same group of patients.


  • Cross-Sectional Study the observation of a defined population at a single point in time or time interval. Exposure and outcome are determined simultaneously. See also glossary of study designs. Decision Analysis is the application of explicit, quantitative methods to analyse decisions under conditions of uncertainty.


  • Ecological Survey: based on aggregated data for some population as it exists at some point or points in time; to investigate the relationship of an exposure to a known or presumed risk factor for a specified outcome.


  • EER Experimental Event Rate: see Event Rate.


  • Event Rate is the proportion of patients in a group in whom an the event is observed. Thus, if out of 100 patients, the event is observed in 27, the event rate is 0.27. Control Event Rate (CER) and Experimental Event Rate (EER) are used to refer to this in control and experimental groups of patients respectively.


  • Evidence-Based Health Care extends the application of the principles of Evidence-Based Medicine (see below) to all professions associated with health care, including purchasing and management.


  • Evidence-Based Medicine is the conscientious, explicit and judicious use of current best evidence in making decisions about the care of individual patients. The practice of evidence-based medicine means integrating individual clinical expertise with the best available external clinical evidence from systematic research. See also the article on EBM: What it is and what it isn't


  • Likelihood Ratio is the likelihood of a given test result in a patient with the target disorder compared to the likelihood of the same result in a patient without that disorder.


  • Meta-analysis is a systematic review or overview, which uses quantitative methods to summarise the results.


  • N-of-1 Trials The patient undergoes pairs of treatment periods organised so that one period involves the use of the experimental treatment and one period involves the use of an alternate or placebo therapy. The patients and physician are blinded, if possible, and outcomes are monitored. Treatment periods are replicated until the clinician and patient are convinced that the treatments are definitely different or definitely not different.


  • Negative Predictive Value (-PV) is the proportion of people with a negative test who are free of disease.


  • Number Needed to Treat (NNT) is the number of patients who need to be treated to prevent one bad outcome. It is the inverse of the ARR: NNT = 1/ARR.


  • Odds Ratio is the odds of an experimental patient suffering an event relative to the odds of a control patient.


  • Overview is a systematic review and summary of the medical literature.


  • P-value is the probability of obtaining the same or more extreme data assuming the null hypothesis of no effect; p-values are generally (but arbitrarily) considered significant if p < 0.05.


  • Positive Predictive Value (+PV) is the proportion of people with a positive test who have disease. Also called the post-test probability of disease after a positive test.


  • Post­test probability: the proportion of patients with that particular test result who have the target disorder (post­test odds/ [1 + post­test odds]).


  • 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. See also glossary of study designs.


  • Relative Risk Reduction (RRR) is the percent reduction in events in the treated group event rate (EER) compared to the control group event rate (CER): RRR = (CER - EER) / CER * 100


  • Risk Ratio is the ratio of risk in the treated group (EER) to the risk in the control group (CER): RR = EER/CER. RR is used in randomised trials and cohort studies.


  • Significance comes in 2 varieties:statistical significance is when the p-value is small enough to reject the null hypothesis of no effect; whereclinical significance is when the effect size is large enough to be potentially considered worthwhile by patients.


  • Sensitivity is the proportion of people with disease who have a positive test.


  • SnNout when a sign/test has a high sensitivity, a negative result rules out the diagnosis; e.g. the sensitivity of a history of ankle swelling for diagnosing ascites is 92 per cent, therefore is a person does not have a history of ankle swelling, it is highly unlikely that the person has ascites.


  • Specificity is the proportion of people free of a disease who have a negative test.


  • SpPin when a sign/test has a high specificity, a Positive result rules in the diagnosis; e.g. the specificity of fluid wave for diagnosing ascites is 92 per cent. Therefore, if a person has a fluid wave, it is highly likely t hat the person has ascites.


  • Systematic Review is a literature review focused on a single question which tries to identify, appraise, select and synthesise all high quality research evidence relevant to that question. 


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