This glossary is intended to provide guidance as to the meanings of EBM terms. If you would like to comment on any of the entries given, please be encouraged to do so.

Absolute Risk Reduction (ARR) is the difference in the event rate between control group (CER) and treated group (EER): ARR = CER - EER.
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. See also glossary of study designs.

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. See also glossary of study designs.

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 Survery: 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 Experiemental 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 wi th 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 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. See also Calculating Sensitivity and Specificity and on samples of Likelihood Ratios.

Meta-analysis is an 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 epxerimental 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 htat 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. See also Calculating Sensitivity and Specificity.

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.

See also section on NNTs.

Odds are a ratio of events to non-events. If the event rate for a disease is 0.1 (10 per cent), its nonevent rate is 0.9 and therefore its odds are 1:9, or 0.111. Note that this is not the same expression as the inverse of event rate.

Odds Ratio describes the odds of an experimental patient suffering an adverse event relative to a control patient. See also section on Odds Ratios.

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

Positive Predictive Value (+PV) is the proportion of people with a positive test who have disease. See also Calculating Sensitivity and Specificity.

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.

Sensitivity is the proportion of people with disease who have a positive test. See also Calculating Sensitivity and Specificity.

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. See also section on SpPins and SnNouts.

Specificity is the porportion of people free of a disease who have a negative test. See also Calculating Sensitivity and Specificity.

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. See also section on SpPins and SnNouts.