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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Haplotype
Alleles that tend to occur together on the same chromosome due to single-nucleotide polymorphisms (SNPs) being in proximity and therefore inherited together.

Hardy-Weinberg equilibrium (HWE)
A situation in which a defined population displays constant genotype frequencies from generation to generation, and those genotype frequencies can be calculated from the allele frequencies based on the HWE formula.

Harm
1. Adverse consequences of exposure to a stimulus. 2. Adverse consequences of exposure to an intervention.

Hawthorne effect
The tendency for human performance to improve when participants are aware that their behavior is being observed.

Hazard ratio
The weighted relative risk of an outcome (eg, death) over the entire study period; often reported in the context of survival analysis.

Health
A state of optimal physical, mental, and social well-being; not merely the absence of disease and infirmity (World Health Organization definition).

Health care personnel
Such persons include Physicians (Internists-UK), Medical Doctors (specific non-internists-UK), Nurses (including Nurse Practitioners and Physician Assistants) and other allied health personnel. See also Health professionals.

Health condition
A broad term for a health state that may include diseases, disorders, syndromes, and symptoms. See also Health state.

Health costs
Health care resources that are consumed. These reflect the inability to use the same resources for other worthwhile purposes (opportunity costs).

Health outcomes
All possible changes in health status that may occur for a defined population or that may be associated with exposure to an intervention. These include changes in the length and quality of life, major morbid events, and mortality.

Health professionals
All persons with health-based certification: physicians, nurses, medical doctors, physiotherapists, pharmacists, occupational therapists, respiratory technicians, and counselors. See also Health care personnel.

Health profile
A type of data collection tool, intended for use in the entire population (including the healthy, the very sick, and patients with any sort of health problem) that attempts to measure all important aspects of health-related quality of life (HRQL). See also Health-related quality of life.

Health state
The health condition of an individual or group over a specified interval of time (commonly assessed at a particular point in time).

Health-related quality of life
Measurements of how people are feeling, or the value they place on their health state. Such measurements can be disease specific or generic. See also Health profile.

Hegar sign
A palpable softening of the lowermost portion of the corpus occurring at about 6 weeks' gestational age. To elicit this sign, when the uterus is anteverted, the examiner places two fingers in the anterior vaginal fornix (or the posterior fornix in the presence of a retroverted uterus) and the compresses behind the fundus at the lower uterine segment with the other hand, using suprapubic pressure.

Heterogeneity
Differences among individual studies included in a systematic review, typically referring to study results; the terms can also be applied to other study characteristics.

Heterozygous
An individual is heterozygous at a gene location if he or she has 2 different alleles (one on the maternal chromosome and one on the paternal) at that location.

Hierarchical regression
Hierarchical regression examines the relation between independent variables or predictor variables (eg, age, sex, disease severity) and a dependent variable (or outcome variable; eg, death, exercise capacity). Hierarchical regression differs from standard regression in that one predictor is a subcategory of another predictor. The lower-level predictor is nested within the higher-level predictor. For instance, in a regression predicting likelihood of withdrawal of life support in intensive care units (ICUs) participating in an international study, city is nested within country and ICU is nested within city.

Hierarchy of evidence
A system of classifying and organizing types of evidence, typically for questions of treatment and prevention. Clinicians should look for the evidence from the highest position in the hierarchy.

Historical cohort design
Cohort studies can be conducted retrospectively (historically) in the sense that someone other than the investigator has followed patients, and the investigator obtains the data base and then examines the association between exposure and outcome.

Historiography
A qualitative research methodology concerned with understanding both historical events and approaches to the writing of historical narratives.

Homans sign
The development of pain in the calf or popliteal region on forceful and abrupt dorsiflexion of the ankle while the knee is flexed.

Homozygous
An individual is homozygous at a gene location if he or she has 2 identical alleles at that location.

Hoyne sign
In patients with severe meningeal irritation, the patient may spontaneously assume the tripod position (also called Amoss sign or Hoyne sign), sitting on the edge of the bed with the knees and hips flexed, the back arched lordotically, the neck extended, and the arms brought back to support the thorax.

Hypoxemia
Deficient oxygenation of the blood.