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.

Headache
Pain in the head; also called cephalalgia.

Headache disorders
Include tension, migraine, or cluster.

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 disparities
Differences in the quality of health care across racial, ethnic, sexual orientation, and socioeconomic groups.

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 care proxy
Also known formally as a durable power of attorney for health care, a type of advance directive that names a proxy to make health care decisions should the patient be incapacitated, based on the patient’s best interests, preferably based on the patient’s previously expressed wishes.

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 Insurance Portability and Accountability Act (HIPAA)
Enacted by the US Congress, HIPAA protects health insurance coverage for workers and their families when they change or lose their jobs and requires the establishment of national standards for electronic health care transactions and national identifiers for providers, health insurance plans, and employers to protect patients’ privacy.

Health literacy
The degree to which individuals have the capacity to obtain, process, and understand basic health information and services needed to make appropriate health decisions.

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.

Hearing Handicap Inventory for the Elderly (HHIE-S)
The most commonly used test to quantify hearing handicap. This test has also been used to screen individuals for hearing impairment. The HHIE-S is a 10-item, self-administered questionnaire developed to measure social and emotional handicap secondary to hearing impairment. The HHIE-S can be administered easily in a primary care office setting.

Hearing impairment, conductive
Conductive hearing loss results from pathologic changes of either the external or the middle ear structures, preventing the sound waves from reaching the fluids of the inner ear.

Hearing impairment, sensorineural
Sensorineural hearing loss results from pathologic changes of inner ear structures such as the cochlea or the auditory nerve and prevents neural impulses from being transmitted to the auditory cortex of the brain.

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.

Hemodialysis
A method for filtering blood to remove waste products such as creatinine and urea, as well as free water, when the kidneys have failed.

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.

Highly active antiretroviral therapy (HAART)
Combinations of several antiviral medications taken for the treatment of infection by human immunodeficiency virus and other retroviruses.

Hispanic Americans
Persons of Latin American or Spanish descent living in the United States.

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.

Homeless persons
Individuals with no homes or places of residence.

Homogeneity
The inverse of heterogeneity. See also Heterogeneity.

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

Hopkins Competency Assessment Test (HCAT)
A screening instrument for medical decision-making capacity involving an essay, read aloud and written at 3 different reading levels, that explains informed consent, the patient's right to make decisions, factors that impair decision-making ability, and the patient's right to an advance directive. The essay is followed by 6 scored questions to assess capacity.

Hospice care
A facility or program designed to provide a caring environment for meeting the physical, psychological, spiritual, and social needs of the terminally ill and their loved ones.

Hospital diagnosis-related groups (DRGs)
A system created to classify the diseases of hospitalized patients into 1 of approximately 500 groups. DRGs are used to determine how much Medicare pays the hospital for the care of patients within each group, who are assumed to be clinically similar and thus expected to use the same level of hospital resources. For more information, see the following Web site for the system: http://oig.hhs.gov/oei/reports/oei-09-00-00200.pdf.

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.