Glossary
Welcome to the CEBM Glossary.
Key Terms in EBP
Therapeutics
Allocation concealed-deemed to have taken adequate measures to conceal allocation to the study group assignments from those responsible for assessing patients for entry in the trial (eg central randomisation, sealed envelopes, numbered or coded bottles and containers, or other descriptions that contain elements convincing of concealment)
Allocation not concealed-deemed not to have taken adequate measures to conceal allocation to study group assignments from those responsible for assessing patients for entry in the trial (eg no concealment procodures were undertaken, sealed envelopes that were not opaque, or other descriptions that contained elements not convincing of concealment).
Unclear allocation concealment-the authors of the article did not report or provide us with a description of the allocation concealment approach that allowed for classification as concealed or not concealed.
Blinded-any or all of the clinicians, patients, participants, outcome assessors, or statisticians were unaware of who received which study intervention. Those that are blinded are indicated in parentheses. If "initially" is indicated (eg blinded [patients and outcome assessor initially] the code was broken during the trial, for example because of adverse events.
Blinded (unclear)-the authors did not report or provide us with an indication of who, if anyone, was unaware of who received which study intervention.
Unblinded-all participants in the trial (clinicans, patients, participants, outcome assessors, and statisticians) were aware of who received which study intervention.
Diagnostics
Diagnostic Standard - the means used to confirm the presence or absence of the target disorder (“gold” or “reference” standard).
Sensitivity - the proportion of individuals with the target disorder who have a positive test: a/(a+b) = 731/(731+78) = 90%.
Specificity - the proportion of individuals without the target disorder who have a negative test: d/(b+d) = 1500/(270+1500) = 85%
Pre-test Probability (prevalence): the proportion of individuals who have the target disorder, as determined before the test is carried out: (a+c)/(a+b+c+d) = (731 + 78)/(731+270+78+1500) = 32%
Pre-test odds: the odds that the patient has the target disorder before the test is carried out (pretest probability/[1-pretest probability]).
Post-test Probability for any test result: the proportion of individuals with that test result who have the target disorder, after the test is carried out and dependent on its result;
-for a positive test (Positive Predictive Value): a/(a+b) = 731/(731+270) = 73%
Post test odds: the odds that the patient has the target disorder after the test has been carried out (pre test odds X likelihood ratio)
Negative Predictive Value: the proportion of individuals with negative test results who do not have the target disorder: d/(c+d) = 1500/(78+1500) = 95%When the experimental treatment reduces the link for a bad event
Likelihood Ratio for any test result (including multiple levels of the test result): the ratio of the probability of that test result among individuals with the target disorder to the probability of that same test result among individuals who are free of the target disorder.
-for a positive test result = LR+ = sensitivity/(1-specificity)
-for a negative test result = LR- = (1-sensitivity)/specificity
Absolute Risk Reduction (ARR)-The ARR is the absolute arithmetic difference in event rates of an adverse event of interest between control group (CER) and experimental group (EER) when the experimental treatment prevents harm occurring to more patients than the control treatment.EER-CER
Number needed to treat (NNT)-The NNT is the number of patients that need to be treated to prevent one additional adverse outcome. This is the inverse of the absolute risk reduction. Calculated as 1/ARR rounded up to the next whole number and accompanied by its 95% CI.
When the experimental treatment increases the probability of a good event
Relative Benefit increase (RBI)- the increase in the rates of good events, comparing experimental and control patients in a trial. Calculated as [EER-CER]/CER
Absolute Benefit Increase (ABI)-the absolute arithmetic difference in event rates, [EER-CER]
NNT-calculated as 1/ABI; denotes the number of patients who must receive the experimental treatment to create one additional improved outcome in comparison with the control treatment.
When the experimental treatment increases the probability of a bad event
Relative risk increase(RRI) - the increase in rates of bad events, comparing experimental patients to control patients in a trial, and calculated as for RBI. RRI is also used in assessing the effect of risk factors for the disease.
Absolute risk increase (ARI)- the absolute difference in rates of bad events, when the experimental treatment harms more patients that the control treatment; calculated as for ABI.
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.
Confidence Interval (CI)- the CI quanifies 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.
Weighted Event rates-the contributions of individual studies to the total in a meta-analysis, determined by the sample size and the number of events in each study.
If you don't find your answer here, try the STEPS statistical glossary.
