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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Candidate gene study
A study that evaluates association of specific genetic variants with outcomes or traits of interest, selecting the variants to be tested according to explicit considerations (known or postulated biology or function, previous studies, etc).

Cardiac tamponade
Cardiac tamponade occurs when fluid trapped in the pericardial space compresses the heart and compromises cardiac output. The consequences of cardiac tamponade range from barely detectable effects to overt hemodynamic collapse.

Case reports
Descriptions of individual patients.

Case series
A report of a study of a collection of patients treated in a similar manner, without a control group. For example, a clinician might describe the characteristics of an outcome for 25 consecutive patients with diabetes who received education for prevention of foot ulcers.

Case study
In qualitative research, an exploration of a case defined by some boundaries or contemporary phenomena usually within a real-life context.

Case-control study
A study designed to determine the association between an exposure and outcome in which patients are sampled by outcome. Those with the outcome (cases) are compared to those without the outcome (controls) with respect to exposure to the suspected harmful agent.

Castell sign
A sign that indicates splenomegaly. The patient is placed in the supine position. Percussion is carried out in the lowest intercostal space in the left anterior axillary line in both expiration and full inspiration. In a normal expiration result, the percussion note remains resonant throughout this maneuver. Splenomegaly is diagnosed when the percussion note is dull or becomes dull on full inspiration.

Categorical variable
A categorical variable may be nominal or ordinal. Categorical variables can be defined according to attributes without any associated order (eg, medical admission, elective surgery, or emergency surgery); these are called nominal variables. A categorical variable can also be defined according to attributes that are ordered (eg, height such as high, medium, or low); these are called ordinal variables.

CDSS intervention
A clinical decision support system (CDSS) intervention is used with individual patients to guide diagnosis and therapy, plus provide feedback on performance and tips on patient management.

Chadwick sign
When the mucous membranes of the vulva, vagina, and cervix become congested and take on a bluish-violet hue.

Chance-corrected agreement
The proportion of possible agreement achieved beyond what one would expect by chance alone, often measured by the kappa statistic.

Chance-independent agreement
The proportion of possible agreement achieved that is independent of chance and unaffected by the distribution of ratings, as measured by the φ statistic.

Channeling bias
Tendency of clinicians to prescribe treatment based on a patient’s prognosis. As a result of the behavior, in observational studies, treated patients are more or less likely to be high-risk patients than untreated patients, leading to biased estimate of treatment effect. See also Bias.

Checklist effect
1. The effect on clinicians’ behavior of having them record information, or their orders, using a structured data collection form. 2. The improvement seen in medical decision making because of more complete and structured data collection (eg, clinicians fill out a detailed form, so their decisions improve).

Chi-square test
A nonparametric test of statistical significance used to compare the distribution of categorical outcomes in two or more groups, the null hypothesis of which is that the underlying distributions are identical.

Chromosome
Self-replicating structures in the nucleus of a cell that carry the genetic information.

Circumcision
The cutting off of the foreskin of males as a sanitary measure in modern surgery or as a religious rite.

Cirrhosis
Widespread disruption of normal liver structure by fibrosis and the formation of regenerative nodules that is caused by various chronic progressive conditions affecting the liver (such as long-term alcohol abuse or hepatitis).

Clinical decision support system
A strategy for changing clinician behavior. An information system used to integrate clinical and patient information and provide support for decision-making in patient care. See also Computer decision support system.

Clinical gestalt
The physician's overall intuitive sense of the likelihood of disease established after the clinical evaluation of the patient. The clinical evaluation may include risk factors, history, symptoms, signs, and basic laboratory or radiological studies.

Clinical practice guidelines
A strategy for changing clinician behavior. Systematically developed statements or recommendations to assist practitioner and patient decisions about appropriate health care for specific clinical circumstances. They present indications for performing a test, procedure, or intervention, or the proper management for specific clinical problems. Guidelines may be developed by government agencies, institutions, organizations such as professional societies or governing boards, or by convening expert panels.

Clinical prediction rules
A guide for practice that is generated by initially examining, and ultimately combining, a number of variables to predict the likelihood of a current diagnosis or a future event. Sometimes, if the likelihood is sufficiently high or low, the rule generates a suggested course of action.

Clock-Drawing Test
A test of executive functioning where a patient is asked to draw an analog clock.

Closed fist sign
Paresthesias in the distribution of the median nerve when the patient actively flexes the fingers into a closed fist for 60 seconds.

Cluster analysis
A statistical procedure in which the unit of analysis matches the unit of randomization, which is something other than the patient or participant (eg, school, clinic).

Cluster assignment
The assignment of groups (eg, schools, clinics) rather than individuals to intervention and control groups. This approach is often used when assignment by individuals is likely to result in contamination (eg, if adolescents within a school are assigned to receive or not receive a new sex education program, it is likely that they will share the information they learn with one another; instead, if the unit of assignment is schools, entire schools are assigned to receive or not receive the new sex education program). Cluster assignment is typically randomized, but it is possible (though not advisable) to assign clusters to treatment or control by other methods.

Cluster-type headache
Headache that presents as excruciating pain around the eye and temple and comes and goes in a “cluster” like pattern.

Cochrane Q
A common test for heterogeneity that assumes the null hypothesis that all the apparent variability between individual study results is due to chance. Cochrane Q generates a probability, presented as a P value, based on a ² distribution, that between-study differences in results equal to or greater than those observed are likely to occur simply by chance.

Cognition disorders
Disorders such as dementia and delirium that involve mental activities associated with thinking, learning, and memory.

Cohort
A group of persons with a common characteristic or set of characteristics. Typically, the group is followed for a specified period of time to determine the incidence of a disorder or complications of an established disorder (prognosis). See also Cohort study.

Cohort study
Study of a group of individuals, some of whom are exposed to a variable of interest (eg, a drug treatment or environmental exposure), in which participants are followed up over time to determine who develops the outcome of interest and whether the outcome is associated with the exposure.

Cointerventions
Intervention other than intervention under study that affect the outcome of interest and that may be differentially applied to intervention and control groups and, thus, potentially bias the results of a study.

Comorbidity
Disease(s) or conditions that coexist(s) in study participants in addition to the index condition that is the subject of the study.

Complete follow-up
The investigators are aware of the outcome in every patient who participated in a study.

Composite endpoint
When investigators measure the effect of treatment on an aggregate of endpoints of various importance. Inferences from composite endpoints are strongest in the rare situations in which (1) the component endpoints are of similar patient-importance, (2) the endpoints that are more important occur with at least similar frequency to those that are less important, and (3) strong biologic rationale supports results that, across component endpoints, show similar relative risks with sufficiently narrow confidence intervals.

Computer decision support system
A strategy for changing clinician behavior. Computer-based information systems used to integrate clinical and patient information and provide support for decision making in patient care. In clinical decision support systems (CDSSs) that are computer based, detailed individual patient data are entered into a computer program and are sorted and matched to programs or algorithms in a computerized database, resulting in the generation of patient-specific assessments or recommendations. CDSSs can have the following purposes: alerting, reminding, critiquing, interpreting, predicting, diagnosing, and suggesting. See also Clinical decision support system.

Concealment
Randomization is concealed if the person who is making the decision about enrolling a patient is unaware of whether the next patient enrolled will be entered in the intervention or control group (using techniques such as central randomization or sequentially numbered opaque, sealed envelopes). If randomization is not concealed, patients with better prognoses may tend to be preferentially enrolled in the active intervention arm, resulting in exaggeration of the apparent benefit of intervention (or even falsely concluding that the intervention is efficacious). See also Blind.

Concepts
The basic building blocks of theory.

Conceptual framework
An organization of interrelated ideas or concepts that provides a system of relationships between those ideas or concepts.

Conditional probabilities
The probability of a particular state, given another state (i.e., the probability of A, given B).

Confidence interval
Range between two values within which it is probable that the true value lies for the whole population of patients from which the study patients were selected.

Conflict of interest
A conflict of interest exists when investigators, authors, institutions, reviewers, and/or editors have financial or nonfinancial relationships with other persons or organizations (eg, study sponsors) or personal investments in research projects or the outcomes of projects that may inappropriately influence their interpretation or actions. Conflicts of interest can lead to biased design, conduct, analysis, and interpretation of study results.

Confounder
1. A factor that distorts the true relationship of the study variable of interest by virtue of also being related to the outcome of interest. Confounders are often unequally distributed among the groups being compared. Randomized studies are less likely to have their results distorted by confounders than are observational studies. 2. A factor that is associated with the outcome of interest and is differentially distributed in patients exposed and unexposed to the outcome of interest.

Consecutive sample
A sample in which all potentially eligible patients seen over a period of time are enrolled. See also Case series.

Construct validity
A construct is a theoretically derived notion of the domain(s) we wish to measure. An understanding of the construct will lead to expectations about how an instrument should behave if it is valid. Construct validity therefore involves comparisons between measures and examination of the logical relationships, which should exist between a measure and characteristics of patients and patient groups.

Contamination
Occurs when participants in either the experimental or control group receive the intervention intended for the other arm of the study.

Continuous variable
A variable that can theoretically take any value and in practice can take a large number of values with small differences between them (eg, height). Continuous variables are also sometimes called interval data.

Control group
A group that does not receive the experimental intervention. In many studies, the control group receives either usual care or a placebo.

Convenience sample
Individuals or groups selected at the convenience of the investigator or primarily because they were available at a convenient time or place.

Corollary orders
Orders that are needed to detect or ameliorate adverse reactions.

Correlation
The magnitude of the relationship between two different variables or phenomena.

Correlation coefficient
A numerical expression of the magnitude and direction of the relationship between two variables, which can take values from –1.0 (perfect negative relationship) to 0 (no relationship) to 1.0 (perfect positive relationship).

Cost analysis
An economic analysis in which only costs of various alternatives are compared. This comparison informs only the resource-use half of the decision (the other half being the expected outcomes).

Cost-benefit analysis
An economic analysis in which both the costs and the consequences (including increases in the length and quality of life) are expressed in monetary terms.

Cost-effectiveness acceptability curve
The cost-effectiveness acceptability is plotted on a graph that relates the maximum one is willing to pay for a particular treatment alternative (eg, how many dollars one is willing to pay to gain 1 life-year) on the x-axis to the probability that a treatment alternative is cost-effective compared with all other treatment alternatives on the y-axis. The curves are generated from uncertainty around the point estimates of costs and effects in trial-based economic evaluations or uncertainty around values for variables used in decision analytic models. As one is willing to pay more for health outcomes, treatment alternatives that initially might be considered unattractive (eg, a high cost per life-year saved) will have a higher probability of becoming more cost-effective. Cost-effectiveness acceptability curves are a convenient method of presenting the effect of uncertainty on economic evaluation results on a single figure instead of through the use of numerous tables and figures of sensitivity analyses.

Cost-effectiveness analysis
An economic analysis in which the consequences are expressed in natural units. Examples include cost per life saved or cost per unit of blood pressure lowered.

Cost-effectiveness efficiency frontier
The cost and effectiveness results of each treatment alternative from an economic evaluation can be graphed on a figure known as the cost-effectiveness plane. The cost-effectiveness plane plots cost on the vertical axis (i.e., positive infinity at the top and negative infinity and the bottom) and effects such as life-years on the horizontal axis (i.e., negative infinity at the far left and positive infinity at the far right). One treatment alternative such as usual care is plotted at the origin (i.e., 0, 0), and all other treatment alternatives are plotted relative to the treatment at the origin. Treatment alternatives are considered dominated if they have both higher costs and lower effectiveness relative to any other. Line segments can be drawn connecting the nondominated treatment alternatives and the combination of line segments that join these nondominated treatment alternatives is referred to as the cost-effectiveness efficiency frontier. Constructed in this way, any treatment alternative that lies above the cost-effectiveness efficiency frontier is considered to be inefficient (dominated) by a treatment alternative or combination of alternatives on the efficiency frontier.

Cost-minimization analysis
An economic analysis conducted in situations in which the consequences of the alternatives are identical, and the only issue is their relative costs.

Cost-to-charge ratio
Where there is a systematic deviation between costs and charges, an economic analysis may adjust charges using a cost-to-charge ratio to approximate real costs.

Cost-utility analysis
A type of economic analysis in which the consequences are expressed in terms of life-years adjusted by peoples’ preferences. Typically, one considers the incremental cost per incremental gain in quality-adjusted life years (QALYs). See also Quality-adjusted life-year.

Courvoisier sign
A palpable, nontender gallbladder in a patient with jaundice.

Cox regression model
A regression technique that allows adjustment for known differences in baseline characteristics between intervention and control groups applied to survival data. See also Adjusted analysis.

Credibility
In qualitative research, a term used instead of validity to reflect whether the investigators engaged thoroughly and sensitively with the material and whether the investigators’ interpretations are credible. Signs of credibility can be found not only in the procedural descriptions of methodology but also through an assessment of the coherence and depth of the findings reported.

Critical theory
A qualitative research tradition focused on understanding the nature of power relationships and related constructs, often with the intention of helping to remedy systemic injustices in society.

Critiquing
A strategy for changing clinician behavior. A decision support approach in which the computer evaluates a clinician’s decision and generates an appropriateness rating or an alternative suggestion.

Cronbach α coefficient
Cronbach α is an index of reliability homogeneity or internal consistency of items on a measurement instrument. The Cronbach α rises with the magnitude of the interitem correlation and with the number of items.

Cross-product ratio
A ratio of the odds of an event in an exposed group to the odds of the same event in a group that is not exposed.

Cross-sectional study
The observation of a defined population at a single point in time or during a specific time interval. Exposure and outcome are determined simultaneously.

Crossover study
A study design in which all patients are switched, in a specified or random order, to the alternate intervention after a specified period of time. See also Before-after design.

Curtain sign
Also known as "enhanced ptosis" or "paradoxic ptosis", the curtain sign is usually observed in patients with some initial ptosis. The patient looks straight ahead and refrains from blinking. The examiner holds one eye open, which results in the other lid starting to droop more (like a curtain falling).