E

Economic analysis (synonym: economic evaluation)
Comparison of the relationship between costs and outcomes of alternative healthcare interventions. See cost-benefit analysis, cost-effectiveness analysis, and cost-utility analysis.

Effect size

1. A generic term for the estimate of effect of treatment for a study.
2. A dimensionless measure of effect that is typically used for continuous data when different scales (e.g. for measuring pain) are used to measure an outcome and is usually defined as the difference in means between the intervention and control groups divided by the standard deviation of the control or both groups.  See also standardised mean difference.
   

Effectiveness
The extent to which a specific intervention, when used under ordinary circumstances, does what it is intended to do. Clinical trials that assess effectiveness are sometimes called pragmatic or management trials. See also intention-to-treat.

Efficacy
The extent to which an intervention produces a beneficial result under ideal conditions.Clinical trials that assess efficacy are sometimes called explanatory trials and are restricted to participants who fully co-operate.

EMBASE (Excerpta Medica database)
A European-based electronic database of pharmacological and biomedical literature covering 3,500 journals from 110 countries. Years of coverage - 1974 to present.

Empirical
Empirical results are based on experience (or observation) rather than on reasoning alone.

Endpoint
See outcome.

Epidemiology
The study of the health of populations and communities, not just particular individuals.

Equipoise
A state of uncertainty where a person believes it is equally likely that either of two treatment options is better.

Equivalence trial
A trial designed to determine whether the response to two or more treatments differs by an amount that is clinically unimportant. This is usually demonstrated by showing that the true treatment difference is likely to lie between a lower and an upper equivalence level of clinically acceptable differences.  See also non-inferiority trial.

Estimate of effect (synonym: treatment effect)
The observed relationship between an intervention and an outcome expressed as, for example, a number needed to treat to benefit, odds ratio, risk difference, risk ratio, standardised mean difference, or weighted mean difference.  (Also called treatment effect.)

Event rate
See risk.

Experimental intervention
An intervention under evaluation. In a controlled trial, an experimental intervention arm is compared with one or more control arms, and possibly with additional experimental intervention arms.

Experimental study
the investigators actively intervene to test a hypothesis.  In a controlled trial, one type of experiment, the people receiving the treatment being tested are said to be in the experimental group or arm of the trial.

Explanatory trial
A trial that aims to test a treatment policy in an ideal situation where patients receive the full course of therapy as prescribed, and use of other treatments may be controlled or restricted.  See also pragmatic trial.

External validity (synonyms: external validity, generalisability, relevance, transferability)
The extent to which results provide a correct basis for generalisations to other circumstances. For instance, a meta-analysis of trials of elderly patients may not be generalisable to children. (Also called generalisability or applicability.)