JAMAevidence Glossary

Terms are derived from Users' Guides to the Medical Literature: A Manual for Evidence-Based Practice, 2nd Edition and The Rational Clinical Examination: Evidence-Based Clinical Diagnosis. Updated March 2010.
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Ecological study
Ecologic studies examine relationships between groups of individuals with exposure to a putative risk factor and an outcome. Exposures are measured at the population, community, or group level rather than at the individual level. Ecologic studies can provide information about an association; however, they are prone to bias: the ecologic fallacy. The ecologic fallacy holds that relationships observed for groups necessarily hold for individuals (eg, if countries with more dietary fat have higher rates of breast cancer, then women who eat fatty foods must be more likely to get breast cancer). These inferences may be correct but are only weakly supported by the aggregate data.

Economic analysis
1. A set of formal, quantitative methods used to compare two or more treatments, programs, or strategies with respect to their resource use and their expected outcomes. 2. Comparative analysis of alternative courses of action in terms of both their costs and consequences.

Educational meetings
A strategy for changing clinician behavior. Participation of professionals in workshops that include interaction and discussion.

Educational outreach visits
See Academic detailing.

Effect size
The difference in outcomes between the intervention and control groups divided by some measure of variability, typically the standard deviation.

Efficiency
Technical efficiency is the relationship between inputs (costs) and outputs (in health, quality-adjusted life-years [QALYs]). Interventions that provide more QALYs for the same or fewer resources are more efficient. Technical efficiency is assessed using cost minimization, cost-effectiveness, and cost-utility analysis. Allocative efficiency recognizes that health is not the only goal that society wishes to pursue, so competing goals must be weighted and then related to costs. This is typically done through cost-benefit analysis.

Efficiency frontier
When the cost and effectiveness results of an economic evaluation are graphed on a cost-effectiveness plane along with incremental cost-effectiveness ratios, the resultant line segments are referred to as the efficiency frontier. Any strategy that has a base-case cost-effectiveness that is above the efficiency frontier would be considered dominated.

Electrical alternans
Changes in the amplitude or morphology of the P, QRS, and ST-T waves from one beat to the next, resulting from cardiac oscillation within the pericardial fluid.

Endpoint
Health event or outcome that leads to completion or termination of follow-up of an individual in a trial or cohort study (eg, death or major morbidity). See also Treatment target.

Equivalence studies
Trials that estimate treatment effects that exclude any patient-important superiority of interventions under evaluation. Equivalence trials require a priori definition of the smallest difference in outcomes between these interventions that patients would consider large enough to justify a preference for the superior intervention (given the intervention's harms and burdens). The confidence interval for the estimated treatment effect at the end of the trial should exclude that difference for the authors to claim equivalence (i.e., the confidence limits should be closer to zero than the minimal patient-important difference). This level of precision often requires investigators to enroll large numbers of patients with large numbers of events. Equivalence trials are helpful when investigators want to see whether a cheaper, safer, simpler (or increasingly often, better method to generate income for the sponsor) intervention is neither better nor worse (in terms of efficacy) than a current intervention. Claims of equivalence are frequent when results are not significant, but one must be alert to whether the confidence intervals exclude differences between the interventions that are as large as or larger than those patients would consider important. If they do not, the trial is indeterminate rather than yielding equivalence.

Erythema migrans
A red rash that expands over time and that occurs at the site of a tick bite. The rash may have an area of central clearing. Lyme disease is the most common cause of erythema migrans.

Ethnography
In qualitative research, an approach to inquiry that focuses on the culture or subculture of a group of people to try to understand the world view of those under study.

Event rate
Proportion or percentage of study participants in a group in which an event is observed. Control event rate (CER) and experimental event rate (EER) are used to refer to event rates in control groups and experimental groups of study participants, respectively. See also Treatment effect; Baseline risk.

Evidence
A broad definition of evidence is any empirical observation, whether systematically collected or not. The unsystematic observations of the individual clinician constitute one source of evidence. Physiologic experiments constitute another source. Clinical research evidence refers to systematic observation of clinical events.

Evidence-based experts
Clinicians who can, in a sophisticated manner, independently find, appraise, and judiciously apply the best evidence to patient care.

Evidence-based medicine
1. The conscientious, explicit, and judicious use of current best evidence in making decisions about the care of individual patients. Evidence-based clinical practice requires integration of individual clinical expertise and patient preferences with the best available external clinical evidence from systematic research, and consideration of available resources. 2. Evidence-based medicine (EBM) can be considered a subcategory of evidence-based health care, which also includes other branches of health care practice such as evidence-based nursing or evidence-based physiotherapy. EBM subcategories include evidence-based surgery and evidence-based cardiology. See also Evidence-based practice.

Evidence-based policy making
Policy making is evidence based when practice policies (eg, use of resources by clinicians), service policies (eg, resource allocation, pattern of services), and governance policies (eg, organizational and financial structures) are based on research evidence of benefit or cost-benefit.

Evidence-based practice
The conscientious, explicit, and judicious use of current best evidence in making decisions about the care of individual patients. Evidence-based clinical practice (or evidence-based health care) requires integration of individual clinical expertise and patient preferences with the best available external clinical evidence from systematic research, and consideration of available resources.

Evidence-based practitioners
Clinicians who can differentiate evidence-based summaries and recommendations from those that are not evidence-based and understand results sufficiently well to apply them judiciously in clinical care, ensuring decisions are consistent with patients’ values and preferences.

Exclusion criteria
The characteristics that render potential subjects ineligible to participate in a particular study or that render studies ineligible for inclusion in a systematic review.

Experimental event rate
Proportion or percentage of study participants in the experimental or intervention group in whom an event is observed.

Experimental studies
In contrast with Observational studies, studies in which the investigators control which patients are exposed to health care interventions and which are not exposed or are exposed to alternate (control) interventions.

Experimental therapy
A therapeutic alternative to standard or control therapy, which is often a new intervention or different dose of a standard drug.

Explode
When searching MEDLINE, the “explode” command identifies all articles that have been indexed using a given MeSH term as well as articles indexed using more specific terms.

Exposure
A condition to which patients are exposed (either a potentially harmful agent or a potentially beneficial one) that may have an impact on their health.