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 December 2009.
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Data completeness bias
Using a computer decision support system (CDSS) to log episodes in the intervention group and using a manual system in the non-CDSS control group can create variation in the completeness of data. See also Bias.

Data-dredging
Searching a data set for differences between groups on particular outcomes, or in subgroups of patients, without explicit a priori hypotheses.

de Musset head-bobbing sign
A peripheral hemodynamic sign traditionally associated with aortic regurgitation. The de Musset head-bobbing sign consists of a forward shaking of the head with every heartbeat. It is best observed in patients who are sitting.

Decision aid
A tool that endeavors to present patients with the benefits and harms of alternative courses of action in a manner that is quantitative, comprehensive, and understandable.

Decision analysis
A systematic approach to decision making under conditions of uncertainty. It involves identifying all available alternatives and estimating the probabilities of potential outcomes associated with each alternative, valuing each outcome, and, on the basis of the probabilities and values, arriving at a quantitative estimate of the relative merit of the alternatives.

Decision tree
Most clinical decision analyses are built as decision trees, and the articles usually will include one or more diagrams showing the structure of the decision tree used for the analysis.

Degrees of freedom
A technical term in a statistical analysis that has to do with the power of the analysis. The more degrees of freedom, the more powerful the analysis. The degrees of freedom typically refers to the number of observations in a sample less the number of unknown parameters estimated for the model. It reflects a sort of adjusted sample size, with the adjustment based on the number of unknowns that need to be estimated in a model. For example, in a 2-sample t test, the degrees of freedom is n1 + n2 – 1 – 1, because there are n1 + n2 subjects altogether and 1 mean estimated in one group and 1 mean in another, giving n1 + n2 – 2.

Deontological
A deontological approach to distributive justice holds that the clinician’s only responsibility should be to best meet the needs of the individual under his or her care. An alternative to the consequentialist or utilitarian view.

Detection bias
The tendency to look more carefully for an outcome in one of the comparison groups. Also known as surveillance bias. See also Bias.

Determinants of outcome
The causal factors that most strongly determine whether or not a target event will occur.

Dichotomous outcome
A categorical variable that can take one of two discrete values rather than an incremental value on a continuum (eg, pregnant or not pregnant, dead or alive).

Dichotomous variable
A variable that can take one of two discrete values rather than values incrementally placed along a continuum (eg, male or female, pregnant or not pregnant, dead or alive).

Differential diagnosis
The set of diagnoses that can plausibly explain a patient’s presentation. See also Active alternatives.

Differential verification bias
When test results influence the choice of the reference standard (eg, test-positive patients undergo an invasive test to establish the diagnosis, whereas test-negative patients undergo long-term follow-up without application of the invasive test), the assessment of test properties may be biased. See also Bias; Verification bias.

Dipstick urinalysis
A chemical analysis of urine performed by using urine dipsticks, in which the test results can be read as color changes.

Disability-adjusted life-years
The number of years of life after downward adjustment for disabilities that patients experience. See also Quality-adjusted life-year.

Discriminant analysis
A statistical technique, similar to logistic regression analysis, that identifies variables that are associated with the presence or absence of a particular categorical (nominal) outcome.

Disease-specific health-related quality of life
Disease-specific HRQL measures evaluate the full range of patients’ problems and experiences relevant to a specific condition or disease. See also Health-related quality of life.

Document analysis
In qualitative research, this is one of 3 basic data collection methods. It involves the interpretive review of written material.

Dominant
Describes any trait that is expressed in a heterozygote, ie, one copy of that allele is sufficient to manifest its effect.

Dominate
In economic evaluation, if the intervention of interest is both more effective and less costly than the control strategy, it is said to dominate the alternative.

Dose-response gradient
Exists when the risk of an outcome changes in the anticipated direction as the quantity or the duration of exposure to the putative harmful or beneficial agent increases.

Downstream costs
Costs due to resources consumed in the future and associated with clinical events in the future that are attributable to the intervention.

Drug class effects
Similar effects produced by most or all members of a class of drugs (eg, beta blockers, calcium antagonists, or angiotensin converting enzyme inhibitors).

Dysuria
Painful urination.