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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Sampling error
Error introduced by chance differences between the estimate obtained from the sample and the true value in the population from which the sample was drawn. Sampling error is inherent in the use of sampling methods and is measured by the standard error.

Schamroth sign
Normal fingers create a diamond-shaped window when the dorsal surfaces of the terminal phalanges of similar fingers are opposed. In the clubbed finger, the diamond becomes obliterated because of the loss of the profile angle and the increase in the soft tissue at the cuticle (Schamroth sign).

Screening
Services designed to detect people at high risk of experiencing a condition associated with a modifiable adverse outcome, offered to persons who have neither symptoms of nor risk factors for a target condition.

Secondary care
Medical care provided to a patient when referred by one health professional to another with more specialized qualifications or interests. There are two levels of referred care: secondary and tertiary. Secondary care is usually provided by a broadly skilled specialist such as a general surgeon, general internist or obstetrician. See also Referred care.

Secular trends
Changes in the probability of events with time, independent of known predictors of outcome.

Selective screening
Services to be offered to asymptomatic persons with one or more risk factors for a target condition, such as family history of the disease, certain personal behaviors, or membership in a population with increased prevalence of the disease. See also Screening.

Sensitivity
The proportion of people who truly have a designated disorder who are so identified by the test. The test may consist of, or include, clinical observations. See also Sensitivity analysis; Specificity; SnNout.

Sensitivity analysis
Any test of the stability of the conclusions of a health care evaluation over a range of probability estimates, value judgments, and assumptions about the structure of the decisions to be made. This may involve the repeated evaluation of a decision model in which one or more of the parameters of interest are varied.

Sentinel effect
The tendency for human performance to improve when participants are aware that their behavior is being evaluated; in contrast to the Hawthorne effect, which refers to behavior change as a result of being observed but not evaluated.

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

Sequential tests
Tests conducted in sequence, rather than simultaneously.

Sign
Any abnormality indicative of disease, discoverable by the clinician at an examination of the patient. It is an objective aspect of a disease.

Sign test
A nonparametric test for comparing two paired groups based on the relative ranking of values between the pairs.

Silo effect
One of the main reasons for considering narrower viewpoints in conducting an economic analysis is to assess the impact of change on the main budget holders because budgets may need to be adjusted before a new intervention can be adopted (the silo effect).

Simple regression
Regression when there is only one independent variable under evaluation with respect to a dependent variable. See also Regression.

SnNout
When a test with a high Sensitivity is Negative, it effectively rules out the diagnosis of disease. See also Sensitivity.

Snowball sampling
Study participants nominate or refer other potential study participants who meet the study inclusion criteria.

SNP
Abbreviation for single-nucleotide polymorphism, a single base pair change in the DNA sequence at a particular point compared with the “common” or “wild-type” sequence.

Specificity
The proportion of people who are truly free of a designated disorder who are so identified by the test. The test may consist of, or include, clinical observations. See also Sensitivity; SpPin.

Spectrum bias
Ideally, diagnostic test properties will be assessed in a population in which the spectrum of disease in the target-positive patients includes all those in whom clinicians might be uncertain about the diagnosis, and the target-negative patients include all those with conditions easily confused with the target condition. Spectrum bias may occur when the accuracy of a diagnostic test is assessed in a population that differs from this ideal. Examples of spectrum bias include a situation in which a substantial proportion of the target-positive population have advanced disease, and target-negative participants are normal or asymptomatic. Such situations typically occur in diagnostic case-control studies (eg, comparing those with advanced disease to normal individuals). Such studies are liable to yield an overly sanguine estimate of the usefulness of the test. See also Bias.

SpPin
When a test is highly Specific, a Positive result can rule in the diagnosis. See also Specificity.

Square wrist sign
The anteroposterior dimension of the wrist divided by the mediolateral dimension equals a ratio of greater than 0.70, when measured with calipers at the distal wrist crease.

Standard error
The standard deviation of an estimate of a population parameter. The standard error of the mean is the standard deviation of the estimate of the population mean value.

Standard gamble
A direct preference or utility measure that effectively asks respondents to rate their quality of life on a scale from 0 to 1.0, where 0 is death and 1.0 is full health. Respondents choose between a specified time x in their current health state and a gamble in which they have probability P (anywhere from 0 to 0.99) of full health for time x, and a probability 1 – P of immediate death.

Standards
Authoritative statements of minimal levels of acceptable performance or results, excellent levels of performance or results, or the range of acceptable performance or results.

STARI
Southern tick-associated rash illness (Masters disease).

Statistical inference
Statistical methodologies to make deductions about underlying truth. There are two principle functions: (1) To predict or estimate a population parameter from a sample statistic, and (2) to test statistically based hypotheses.

Statistical significance
A term indicating that the results obtained in an analysis of study data are unlikely to have occurred by chance, and the null hypothesis is rejected. When statistically significant, the probability of the observed results, given the null hypothesis, falls below a specified level of probability (most often P < 0.05).

Stopped early trials
Truncated randomized controlled trials (RCTs) are trials stopped early because of apparent harm because the investigators have concluded that they will not be able to demonstrate a treatment effect (futility), or because of apparent benefit. Believing the treatment from RCTs stopped early for benefit will be misleading if the decision to stop the trial resulted from catching the apparent benefit of treatment at a random high.

Stopping rules
These are methodological and statistical guides that inform decisions to stop trials early. They can incorporate issues such as the planned sample size, planned and conducted interim analyses, presence and type of data monitoring including independent research oversight, statistical boundaries, and statistical adjustments for interim analyses and stopping.

Structured abstracts
These abstracts often include critical information about research conduct omitted from the original reports. They do not include the introduction or the discussion sections of the original report or the conclusions of the original study.

Subgroup analysis
The separate analysis of data for subgroups of patients, such as those at different stages of their illness, those with different comorbid conditions, or those of different ages.

Surrogate outcomes or endpoints
Outcomes that are not in themselves important to patients but are associated with outcomes that are important to patients (eg, bone density for fracture, cholesterol for myocardial infarction, and blood pressure for stroke). These outcomes would not influence patient behavior if they were the only outcomes that would change with an intervention.

Survey
Observational study that focuses on obtaining information about activities, beliefs, preferences, knowledge, or attitudes from respondents through interviewer-administered or self-administered methods.

Survival analysis
A statistical procedure used to compare the proportion of patients in each group who experience an outcome or endpoint at various time intervals over the duration of the study (eg, death).

Survival curve
A curve that starts at 100% of the study population and shows the percentage of the population still surviving (or free of disease or some other outcome) at successive times for as long as information is available.

Symptom
Any phenomenon or departure from the normal in function, appearance, or sensation reported by the patient and suggestive or indicative of disease. Symptoms are considered subjective.

Syndrome
A collection of signs and/or symptoms and/or physiological abnormalities.

Syndrome diagnosis
When no reference standards exist, investigators' degree of diagnostic certainty is much lower. In these situations, known sometimes as syndrome diagnosis, diagnostic criteria usually rely on a list of clinical features required for the diagnosis. See also Syndrome.

Synonymous SNP
A SNP that does not lead to a change in the amino acid sequence compared with the common or wild-type sequence. Compare to nonsynonymous, in which there is a change in the amino acid sequence as a result of the SNP.

Synovial fluid
Fluid found in the cavities of synovial joints.

Systematic review
1. The consolidation of research evidence that incorporates a critical assessment and evaluation of the research (not simply a summary) and addresses a focused clinical question using methods designed to reduce the likelihood of bias. 2. The identification, selection, appraisal, and summary of primary studies addressing a focused clinical question using methods to reduce the likelihood of bias.