Glossary terms for 'E'
|Effect size||In the context of sample size planning, a measure of how big a difference the investigator wishes to detect between the groups that will be compared, or of the size of the association. More generally, the actual size of that difference or association after the study is completed. For example, the investigators based their sample size estimates on an effect size of a 20 mg/dL difference in mean blood glucose levels in the two groups.|
|Effect-cause||The problematic possibility that an outcome causes the predictor, rather than vice-versa. For example, although a case-control study observed that exposure to inhaled bronchodilators was associated with an increased risk of interstitial lung disease, the most likely explanation was effect-cause, namely that patients with interstitial lung disease were more likely to have been treated (erroneously) with inhalers. See also cause-effect.|
|Effect-modification||The condition in which the strength of the association between a predictor and an outcome is affected by a third variable (often called the effect-modifier, though it can be difficult to determine which is the predictor and which the effect-modifier). For example, the investigators found that the effects of income on stroke risk differed in white and blacks, such that poverty had stronger association with stroke in blacks than in whites. See also confounding and interaction.|
|Effectiveness||Although there is no standard definition of this term, we use it to refer to a measure of how well an intervention works in actual practice, as opposed to how well it worked in a randomized trial. For example, because clinical trials have found that tissue plasminogen activator (tPA) reduces morbidity and mortality from stroke in several trials performed in urban settings, the investigators studied its effectiveness in 25 rural emergency rooms. See also efficacy.|
|Efficacy||Although there is no standard definition of this term, we use it to refer to a measure of how well an intervention worked in a clinical trial, as opposed to how well it would work in actual practice. For example, a clinical trial reported that tissue plasminogen activator (tPA) had an efficacy of 25% in reducing morbidity and mortality among patients with acute stroke. See also effectiveness.|
|Entry criteria||A list of the attributes that subjects need to be eligible to participate in a study. The entry criteria may vary if subjects are enrolled in different groups, such as in case-control or double-cohort studies. See also inclusion and exclusion criteria.|
|Epidemiologist||A physician, broken down by age and sex. For example, one of the authors (but we are not saying which one!).|
|Epidemiology||The science of determining the frequency and determinants of diseases or other health outcomes in populations. For example, the study investigated the epidemiology of handgun violence in inner cities.|
|Equipoise||The situation in which it is not known which of two possibilities (Drug X is better than placebo; Drug X is worse than placebo) is more likely to be true. Thus it is ethical to compare Drug X and placebo in a randomized trial. For example, the investigators believed that there was clinical equipoise, since it was not known whether a proposed new treatment for esophageal cancer would results in better outcomes than the current standard of care.|
|Equivalence study||A study whose purpose is to show that two (or more) treatments have similar outcomes; usually, one of the treatments is new, and the other is known to be effective. For example, an equivalence study design was used to compare two antibiotics (new drug A with old drug B) for the treatment of pneumonia. See also non-equivalence study. |
|Exclusion criteria||A list of attributes that prevent a potential subject from being eligible for a study. For example, the exclusion criteria for the study were prior treatment with an antidepressant medication in the previous two years, current use of alpha-blockers or beta-blockers, and an inability to read English at the 6th grade level. See also inclusion criteria. |
|Experiment||In clinical research, a study in which subjects are assigned randomly to one (or more) treatment or comparison groups. Also called a randomized trial. For example, the investigators performed an experiment to determine whether Drug X was better than placebo in the treatment of fibromyalgia.|
|Exposure||A term used to indicate that a study subject has a particular risk factor. For example, exposure to aspirin was defined as taking an average of one or more aspirin tablets (of any size) a week during the previous 6-month period.|
Glossary material from Hulley SB et al. Designing Clinical Research, 4th ed. Philadelphia, Lippincott Williams & Wilkins, 2013.