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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Background questions
These clinical questions are about physiology, pathology, epidemiology, and general management and are often asked by clinicians in training. The answers to background questions are often best found in textbooks or narrative review articles.

Barrel chest sign
The anterior-posterior dimension of the chest increases in relation to the lateral dimensions, giving the shape of a barrel. This occurs in conditions that result in hyperinflation of the lung.

Base case
In an economic evaluation, the base case is the best estimates of each of the key variables that bear on the costs and effects of the alternative management strategies.

Baseline characteristics
Factors that describe study participants at the beginning of the study (eg, age, sex, disease severity); in comparison studies, it is important that these characteristics be initially similar between groups; if not balanced or if the imbalance is not statistically adjusted, these characteristics can cause confounding and can bias study results.

Baseline risk
The proportion or percentage of study participants in the control group in whom an adverse outcome is observed. See also Absolute risk.

Bayesian analysis
An analysis that starts with a particular probability of an event (the prior probability) and incorporates new information to generate a revised probability (a posterior probability). The approach to diagnosis assumes that diagnosticians are intuitive Bayesian thinkers and move from pretest to posttest probabilities as information accumulates.

Beck triad
The classic findings of tamponade as described in 1935 by thoracic surgeon Claude Schaeffer Beck are characterized by decreasing arterial blood pressure, increasing jugular venous pressure, and a small, quiet heart.

Before-after design
Study in which the investigators compare the status of a group of study participants before and after the introduction of an intervention. See also Crossover study.

Bias
A systematic error in the design, conduct, or interpretation of a study that may cause a systematic deviation from the underlying truth (eg, overestimation of a treatment effect because of failure to randomize).

Blind
Patients, clinicians, data collectors, outcome adjudicators, or data analysts unaware of which patients have been assigned to the experimental or control group. In the case of diagnostic tests, those interpreting the test results are unaware of the result of the reference standard or vice versa. See also Concealment.

Boas sign
Originally, this sign referred to point tenderness in the region to the right of the 10th to 12th thoracic vertebrae, but contemporary sources describe hyperesthesia to light touch in the right upper quadrant or infrascapular area.

Boolean operators
Words used when searching electronic databases. These operators are AND, OR, and NOT and are used to combine terms (AND/OR) or exclude terms (NOT) from the search strategy.

Bootstrap technique
A statistical technique for estimating parameters such as standard errors and confidence intervals based on resampling from an observed data set with replacement from the original sample.

Bronchiolitis
Inflammation of the bronchioles.

Brudzinski sign
Meningeal inflammation and irritation that elicits a protective reflex to prevent stretching of the inflamed and hypersensitive nerve roots, which is detectable clinically as neck stiffness or Kernig or Brudzinski signs. A Brudzinski sign (also known as the "nape of the neck" sign) is present when passive neck flexion in a supine patient results in flexion of the knees and hips.