EBM glossary

Here is a list of useful terms for evidence-based medicine revision.


a priori

planned in advance of any data analysis. They are more reliable than post-hoc comparisons.

blinding

A process 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.

observer bias

an error introduced into measurement when assessors overemphasize what they expect to find and fail to notice behaviors they do not expect.  Can also be introduced because researchers see it and interpret it according to what it means to them whereas it may mean something else to the person showing the behavior.

Hawthorne effect

People singled out for a study of any kind may improve their performance or behavior, not because of any specific condition being tested, but simply because of all the attention they receive.

confounding

refers to a situation in which a measure of the effect of an intervention or exposure is distorted because of the association of exposure with other factor(s) that influence the outcome under investigation. This can lead to erroneous conclusions being drawn, particularly in observational studies.

selection bias

refers to systematic differences between comparison groups in prognosis or responsiveness to treatment. Random allocation with adequate concealment of allocation protects against selection bias.

statistical power

The ability of a study to demonstrate an association or causal relationship between two variables, given that an association exists. For example, 80% power in a clinical trial means that the study has a 80% chance of ending up with a p value of less than 5% in a statistical test (i.e. a statistically significant treatment effect) if there really was an important difference (e.g. 10% versus 5% mortality) between treatments. If the statistical power of a study IS low, the study results will be questionable (the study might have been too small to detect any differences). By convention, 80% is an acceptable level of power.

Randomisation

Method analogous to tossing a coin to assign patients to treatment groups (the experimental treatment is assigned if the coin lands heads and a conventional, control or placebo treatment is given if the coin lands tails). Usually done by using a computer that generates a list of random numbers, which can then be used to generate a treatment allocation list.

allocation concealment

A technique used to prevent selection bias by concealing the allocation sequence from those assigning participants to intervention groups, until the moment of assignment. This prevents researchers from (unconsciously or otherwise) influencing which participants are assigned to a given intervention group.

Innumeracy

The inability to think with numbers. Statistical innumeracy is the inability to think with numbers that represent uncertainties. Ignorance of risk, miscommunication of risk, and clouded thinking are forms of this.

Evidence based medicine

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.

Cross sectional study

The observation of a defined population at a signal point in time or time interval. Exposure and outcome are determined simultaneously.

Baseline characteristics

Values of demographic, clinical and other variables collected for each participant at the beginning of the trial, but before the intervention is administered.

Hypothesis

In a trial, a statement relating to the possible different effect of the interventions on an outcome. The null hypothesis of no such effect is amenable to explicit statistical evaluation by a hypothesis test, which generates a P value.

Eligibility criteria

The clinical and demographic characteristics that define those participants eligible to be enrolled in the trial.

Follow-up

A process of periodic contact with participants enrolled in a trial for the purpose of administering the assigned intervention, modifying the course of intervention, observing the effects of the intervention, or for data collection.

Minimization

An assignment strategy, similar in intention to stratification, that ensures excellent balance between intervention groups for specified prognostic factors. The next participant is assigned to whichever group would minimize the imbalance between groups on specified prognostic factors.
An acceptable alternative to random assignment.

Sample size

The number of participants planned to be included in the trial, usually determined using a statistical power calculation. The sample size should be adequate to provide a high probability of detecting as significant an effect size of a given magnitude if such an effect actually exists.

External validity

The extent to which the results of a trial provide a correct basis for generalizations to other circumstances. Also called "generalizability or "applicability".

Internal validity

The extent to which the design and conduct of the trial eliminate the possibility of bias.

Data dredging

The inappropriate (sometimes deliberately so) search for 'statistically significant' relationships in large quantities of data.

Systematic review

a literature review focused on a single question which tries to identify, appraise, select and synthesize all high quality research evidence relevant to that question. These are generally regarded as the highest level of medical evidence.

(source: Bandolier/CONSORT)

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