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JAMAevidence Glossary

Terms are derived from Users' Guides to the Medical Literature: A Manual for Evidence-Based Practice, 2nd Edition, The Rational Clinical Examination: Evidence-Based Clinical Diagnosis and Care at the Close of Life: Evidence and Experience. Updated October 2014.
Download a PDF of the glossary (295 KB). (Adobe Reader is required to open or print PDF files.)

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A surgical procedure involving an incision through the abdominal wall in order to access the abdominal cavity.

Last Acts
A 10-year national communications and education campaign funded by the Robert Wood Johnson Foundation and aimed at improving how US patients, families, health care professionals, and institutions experience the death and dying process.

Law of multiplicative probabilities
The law of multiplicative probabilities for independent events (in which one event in no way influences the other) tells us that the probability of 10 consecutive heads in 10 coin flips can be found by multiplying the probability of a single head (1/2) 10 times over; that is, 1/2 × 1/2 × 1/2, and so on.

Lead time bias
Occurs when outcomes such as survival, as measured from the time of diagnosis, may be increased not because patients live longer, but because screening lengthens the time that they know they have disease. See also Bias.

Leading hypothesis
The clinician’s single best explanation for the patient’s clinical problem(s).

Length time bias
Occurs when patients whose disease is discovered by screening also may appear to do better, or live longer, than people whose disease presents clinically with symptoms. Screening tends to detect disease that is destined to progress slowly and, therefore, has a good prognosis. See also Bias.

Leukocyte count
White blood cell count.

Levels of evidence
A hierarchy of research evidence to inform practice, usually ranging from strongest to weakest.

Levine technique
An approach to wound-swabbing in which the swab is rotated over a 1 x 1-cm area for 5 seconds, using sufficient pressure to extract fluid.

Life Support Preferences/Predictions Questionnaire—modified (LSPQ-m)
A questionnaire with 9 hypothetical illness scenarios used to determine a patient’s treatment preferences.

Likelihood functions
Functions constructed from a statistical model and a set of observed data that give the probability of that data for various values of the unknown model parameters. Those parameter values that maximize the probability are the maximum likelihood estimates of the parameters. See also Likelihood ratio.

Likelihood ratio
The relative odds that a given test result would be expected in a patient with, as opposed to one without, a disorder of interest. As LRs increase above 1, the test result is better at identifying affected patients. As LRs decrease below 1, the test result is better at identifying unaffected patients. An LR+ is the LR for a positive test result, while an LR- is the LR for a negative test result. The LR+ = sensitivity / (1 - specificity), while the LR- = (1 - sensitivity) / specificity.

Likert scales
Scales, typically with three to nine possible values, that include extremes of attitudes or feelings (eg, from totally disagree to totally agree) that respondents mark to indicate their rating. See also Visual analogue scale.

Linear regression
The term used for a regression analysis when the dependent or target variable is a continuous variable, and the relationship between the dependent and independent variables is thought to be linear.

The tendency of genes or other DNA sequences at specific loci to be inherited together as a consequence of their physical proximity on a single chromosome.

Linkage disequilibrium
A measure of association between alleles at different loci.

Liver transplantation
The surgical replacement of a patient’s diseased liver with a donor’s healthy liver, followed by systemic immunosuppression to prevent rejection of the allograft. An established treatment option for end-stage liver disease and acute liver failure.

Living will
A type of advance directive document that provides general directives about the kinds of treatment that a patient wishes health care professionals and caregivers to provide during terminal care, should the patient be incapacitated.

Local consensus process
A strategy for changing clinician behavior. Inclusion of participating clinicians in discussions to create agreement with a suggested approach to change provider practice.

Local opinion leaders
A strategy for changing clinician behavior. These persons are clinician peers who are recognized by their colleagues as model caregivers or who are viewed as having particular content expertise.

The site(s) on a chromosome at which the gene for a particular trait is located or on a gene at which a particular SNP is located.

Logistic regression
1. A multivariate regression analysis that analyzes relationships between multiple independent variables and categorical dependent variables. 2. A regression analysis in which the dependent variable is binary.

Lok index
A score used to help determine the likelihood of cirrhosis. Created from the patient's platelet count, serum aspartate aminotransferase and alanine aminotransferase, and prothrombin international normalized ratio. Uses the same factors as the Bonacini CDS but estimates the probability of cirrhosis through a logistic model. An index less than 0.2 is associated with a decreased likelihood of cirrhosis.

Lost to follow-up
Patients whose status on the outcome or endpoint of interest is unknown.

Lumbar puncture
Lumbar puncture in the subarachnoid space of the spinal cord allows spinal fluid to be sampled, facilitating the diagnosis of various conditions.

Lumley model of network meta-analysis
A frequentist method for multiple treatment comparisons.

Lung diseases, interstitial
A group of lung diseases affecting the interstitium or tissue and space around the air sacs of the lungs, often producing a restrictive ventilatory defect.
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