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OCEBM Table of Evidence Glossary

Authors: Katherine Law and Jeremy Howick

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.


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: The observational epidemiologic study of persons with the disease (or other outcome variable) of interest and a suitable control (comparison, reference) group of persons without the disease. The relationship of an attribute to the disease is examined by comparing the diseased and nondiseased with regard to how frequently the attribute is present or, if quantitative, the levels of the attribute, in each of the groups.

Case-series: A group or series of case reports involving patients who were given similar treatment. Reports of case series usually contain detailed information about the individual patients. This includes demographic information (for example, age, gender, ethnic origin) and information on diagnosis, treatment, response to treatment, and follow-up after treatment. (NCI Dictionary)

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: The analytic method of epidemiologic study in which subsets of a defined population can be identified who are, have been, or in the future may be exposed or not exposed, or exposed in different degrees, to a factor or factors hypothesized to influence the probability of occurrence of a given disease or other outcome. The main feature of cohort study is observation of large numbers over a long period (commonly years) with comparison of incidence rates in groups that differ in exposure levels.

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.

Diagnosis: The process of determining health status and the factors responsible for producing it; may be applied to an individual, family, group or community. The term applied both to the process of determination and to its findings.

Diagnostic Test: Any medical test performed to confirm, or determine the presence of disease in an individual suspected of having the disease, usually following the report of symptoms, or based on the results of other medical tests. Some examples of diagnostic tests include performing a chest x-ray to diagnose pneumonia, and taking skin biopsy to detect cancerous cells. (Harvard Guide to Diagnostic test)

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).

Historically Controlled Study: A control study recruiting control subject(s) for whom data were collected at a time preceding that at which the data are gathered on the group being studied.

Inception cohort study: A group of individuals identified for subsequent study at an early, uniform point in the course of the specified health condition, or before the condition develops.

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

Local and current random census

Local: Of or belonging to or characteristic of a particular locality or
neighbourhood
Current: Occurring in or belonging to the present time
Random sample: A sample that is arrived at by selecting sample units such that each possible unit has a fixed and determinate probability of selection.
Census: An enumeration of a population, originally intended for purposes of taxation and military service. Census enumeration of a population of a population usually records identities of all persons in every place of residence, with age, or birth date, sex, occupation, national origin, language, marital status, income, and relationship to head of household in addition to information on the dwelling place.

Local and current random sample survey

Local: Of or belonging to or characteristic of a particular locality or neighbourhood
Current: Occurring in or belonging to the present time
Random sample: A sample that is arrived at by selecting sample units such that each possible unit has a fixed and determinate probability of selection.
Survey: An investigation in which information is systematically collected but in which the experimental method is not used.

Local non-random sample

Local: Of or belonging to or characteristic of a particular locality or neighbourhood
Non-random sample: A sample selected by a non-random method, and as a result, some elements of the population have no chance of selection. For example, a scheme whereby units are selected purposively would yield a non-random sample. Again, a sample obtained by taking members at fixed intervals on a list is a non-random sample unless the list was arranged in a random order. (OECD)

Mechanism-based reasoning: Involves an inference from mechanisms to claims that an intervention produces a patient-relevant outcome. Such reasoning will involve an inferential chain linking the intervention (such as antiarrhythmic drugs) with a clinical outcome (such as mortality). (Howick)

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

Monitoring Test: Any medical test performed to confirm, or determine the presence of disease in an individual suspected of having the disease, usually following the report of symptoms, or based on the results of other medical tests. Some examples of diagnostic tests include performing a chest x-ray to diagnose pneumonia, and taking skin biopsy to detect cancerous cells. (Harvard Guide to Diagnostic test)

Nested Case-control study: A case control study in which cases and controls are drawn from the population in a cohort study. As some data are already available about both cases and controls, the effects of some potential confounding variables are reduced or eliminated. In this type of case control study, a set of controls is selected from subjects, i.e. non-cases, at risk at the time of occurrence of each case that arises in a cohort, thus allowing for the confounding effect of time in the analysis.

n-of-1 trial: A variation of a randomized controlled trial in which a sequence of alternative treatment regimens is randomly allocated to a patient. The outcomes of regimens are compared, with the aim of deciding on the optimum regimen for the patient.

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.

Observational study: A family of studies in which investigators compare people who take an intervention with those who do not. The investigators neither allocate patients to receive the intervention not administer the intervention. Instead, they compare records of patients who had taken an intervention and been treated in routine practice with similar patients who had not taken the intervention. The most common observational designs are case-studies, case-series, case-control studies, cohort studies, and historically controlled studies. (Howick)

Odds: A ratio of events to non-events. If the event rate for a disease is 0.2 (20%), 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.

Post-marketing surveillance: A procedure implemented after a drug has been licensed for public use, designed to provide information on the actual use of the drug for a given indication and on the occurrence of side effects, adverse reactions, etc. A method for epidemiologic study of adverse drug reactions.

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

Prevention: Prevention refers to measures taken by an individual or a society to prevent disease happening or its consequences. In general, prevention includes a wide range of interventions, aimed at reducing risks to health. These are grouped into three categories:

  • Primary prevention: refers to strategies used to prevent a disease happening in the first place. An example may be salt reduction to prevent an individual becoming hypertensive. Medication can be used in primary prevention such as the use of blood lowering or cholesterol lowering drugs to lower the risk of a stroke or heart attack.
  • Secondary prevention: refers to strategies used in those with an existing disease which prevent recurrence, or significant morbidity. For example, in someone who has a heart attack cholesterol lowering drugs are used to lower the risk of subsequent heart attack and death.
  • Tertiary prevention: refers to the prevention of long term chronic disease progression, physical deterioration and attendant suffering. For example, removing allergens which may aggravate asthmatic patients; screening for eye, renal, eye, and foot problems among diabetics to reduce the risks of complications.

Prognosis: The prospect of survival and recovery from a disease as anticipated from the usual course of that disease or indicated by special features of the case.

Prognostic cohort study:

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).

Randomized trial: An epidemiological experiment in which subjects in a population are randomly allocated into groups, usually called study and control groups, to receive or not receive an experimental preventive or therapeutic procedure, maneuver, or intervention. The results are assessed by rigorous comparison of rates of disease, death, recovery, or other appropriate outcome in the study and control groups.

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: The application of strategies that limit bias in the assembly, critical appraisal, and synthesis of all relevant studies on a specific topic. Systematic reviews focus on peer-reviewed publications about a specific health problem and use rigorous, standardized methods for selecting and assessing articles. A systematic review may or may not include a meta-analysis, which is a quantitative summary of the results.

Treatment benefits: Positive patient-relevant outcome associated with an intervention, quantifiable by epidemiological measures such as absolute risk reduction (ARR) and number needed to treat (NNT).

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.

 

All definitions in the glossary are from:

Last, J. M. (2001) A Dictionary of Epidemiology "" Fourth Edition. Oxford University Press

unless otherwise specified.

Other Sources:

Harvard Health Publication (2010) A Guide to Diagnostic Tests, viewed 23 November 2010
http://www.health.harvard.edu/diagnostic-tests/

Howick, J. (Forthcoming) Resolving the paradoxes in Evidence-Based Medicine. A philosophical inquiry. Blackwell/Wiley

Organisation for Economic Co-operation and Development (OECD) (2010) Glossary of Statistical Terms, viewed 25 November 2010
http://stats.oecd.org/glossary/

National Cancer Institute (NCI) (2010) NCI Dictionary of Cancer Term, viewed 23 November 2010
http://www.cancer.gov/dictionary/?CdrID=44006

 

 

 

 

Page last edited: 04 February 2014