EBM Glossary

Adverse effect

An appreciably harmful or unpleasant reaction, resulting from an intervention related to the use of a medicinal product, which predicts hazard from future administration and warrants prevention or specific treatment or alteration of the dosage regimen or withdrawal of the product.

Adverse event

An adverse outcome occurring during or after the use of a drug or other intervention but not necessarily caused by it.

Safety, tolerability, serious, severe

The safety of an intervention relates to its potential to cause serious adverse effects.
Tolerability relates to medically less important but unpleasant adverse effects of drugs. These include symptoms such as dry mouth, tiredness, etc, that can affect a person's quality of life and willingness to continue the treatment.
A serious adverse effect is one that has significant medical consequences, such as death, permanent disability, prolonged hospitalisation. Indirect adverse effects, such as traffic accidents, violence, and damaging consequences of mood change, can also be serious.
Severe refers to the intensity of a particular adverse effect. For example, a non-serious adverse effect, such as headache, may be severe in intensity (as opposed to mild or moderate). A non-serious effect, such as impotence, can have disastrous consequences for a person's quality of life.

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.

The process used in epidemiological studies and clinical trials in which the participants, investigators and/or assessors remain ignorant concerning the treatments which participants are receiving. The aim is to minimise observer bias, in which the assessor, the person making a measurement, have a prior interest or belief that one treatment is better than another, and therefore scores one better than another just because of that.

In a single blind study it is may be the participants who are are blind to their allocations, or those who are making measurements of interest, the assessors.

In a double blind study, at a minimum both participants and assessors are blind to their allocations.

In some circumstances much more complicated designs can be used, where blinding is described at different levels.

To achieve a double-blind state, it is usual to use matching treatment and control treatments. For instance, the tablets can be made to look the same, or if one treatment uses a single pill once a day, but the other uses three pills at various times, all patients will have to take pills during the day to maintain blinding.
NB: A lack of blinding is a potent source of bias, and open studies or single-blind studies are potential problems for interpreting results of trials.

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

Relative Risk Reduction (RRR)-The proportion of adverse events that would have occurred in the control group that are avoided by the intervention. [EER-CER]/CER and accompanied by a 95% confidence interval (CI)
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.