Basic Concepts and Terminology

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.

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 in making 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.

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 QUALY).

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. Decision Analysis is the application of explicit, quantitative methods to analyze decisions under conditions of uncertainty.

DOEs Disease-Oriented Evidence deals with aspects of pathophysiology, pharmacology, and etiology--increases understanding of disease processes but does not guide the clinician toward achieving the best outcome for the patient.

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 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.

Incidence Rate is the number of new cases during a specific time period/size of the population at risk. In terms of incidence rate, "crude" is the total members at or during a given time; "specific" is the incidence rate divided by categories (age-specific, disease-specific, mortality); "adjusted rate" is the rate adjusted to a standard population based on characteristics which may influence the outcome, e.g. age-adjusted mortality.

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 Biostatistics and Prevention.

Meta-analysis is an overview which uses quantitative methods to summarize the results.

N-of-1 Trials (aka Single Case Methodology) The patient undergoes pairs of treatment periods organized so that one period involves the use of the experimental treatment and one period involves the use of an alternate or placebo therapy. The patient 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. 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

Odds are a ratio of nonevents to 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 9:1. 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 Study Designs.

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

POEMs Patient-Oriented Evidence that Matters are sources of information that are highly relevant, valid, and can be obtained with minimal effort. POEMs articles are printed in each issue of the Journal of Family Practice and serve as the grist for monthly Family Medicine Journal Clubs.

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

Prevalence Rate is the number of existing cases at a specific time/size of the population at risk. In a stable population, Prevalence = Incidence X Duration of Disease. In terms of prevalence rate, "crude" is the total members at or during a given time; "specific" is the prevalence rate divided by categories (age-specific, disease-specific, mortality); "adjusted rate" is the rate adjusted to a standard population based on characteristics which may influence the outcome, e.g. age-adjusted mortality.

Randomized Controlled Clinical Trial a group of patients is randomized 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 randomized trials and cohort studies.

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 percent, therefore, if a person does not have a history of ankle swelling, it is highly unlikely that the person has as cites. See also section on SpPins and SnNouts.

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 percent. Therefore, if a person has a fluid wave, it is likely that the person has ascites.

Contact
Research Director - Dr. Peggy J. Wagner
Email address - pwagner@mail.mcg.edu
(706) 721-7589


Copyright 2008 Medical College of Georgia All rights reserved.	Research/Faculty Dev \| Medical College of Georgia Please email comments, suggestions or questions to: Stan Sulkowski, ssulkowski@mail.mcg.edu.

January 10, 2008