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Access to health care

having the timely use of personal health services to achieve the best health outcomes


the extent to which a measurement or study result correctly represents the characteristic or relationship that is being assessed

Acquired immunodeficiency syndrome (AIDS)

a disease characterized by a marked reduction in CD4+ T lymphocytes and associated defects in immune response caused by the human immunodeficiency virus (HIV)

Active surveillance

a system of data collection in which those responsible for collecting the information go into the community under observation (typically defined by geographic boundaries) to gather data from various sources


a disease of short duration

Adaptive randomized controlled clinical trial

an experimental study in which the collected data are used to guide predefined design adaptations when the trial is in progress


a procedure for overall comparison of two or more populations in which background differences in the distribution of covariables are removed (see also Standardization)

Administrative data

billing data or hospital discharge data that can be used for research on health-related questions, including costs of care

Age adjustment

a procedure used to calculate summary rates for different populations in which underlying differences in the age distributions are removed (see also Age standardization)

Age-specific rate

a rate (usually incidence or mortality) for a particular age group

Age standardization (direct)

a procedure for obtaining a weighted average of age-specific rates in which the weights are selected on the basis of a standard age distribution (e.g., the population of the United States in 2000)

Alpha error

see Type I error

Analytic epidemiology

activities related to the identification of possible determinants of disease occurrence

Analytic study

a research investigation designed to test a hypothesis, often used in reference to a study of an exposure-disease association


a protein, often produced in response to exposure to an antigen that binds to the antigen and thereby stimulates its inactivation by the immune system


a protein, usually foreign in origin, that is capable of generating an immune response in a host animal

Arithmetic mean

see Mean


hardening of the arteries


the extent to which the occurrence of two or more characteristics is linked either through a causal or noncausal relationship

Asymptomatic persons

individuals who have a particular disease but do not manifest abnormalities of function, appearance, or sensation typically associated with that disease

Attack rate

the proportion of persons within a population who develop a particular outcome within a specified period of time

Attributable risk percent

the percentage of the overall risk of a disease outcome within exposed persons, related to the exposure of interest


a mild illness; when applied to an abnormal growth of cells (i.e., a neoplasm), it connotes a slowly progressing defect that is not invading adjacent tissues (in contrast to the rapid growth and invasive behavior of a malignant neoplasm)

Beta error

see Type II error


a nonrandom error in a study that leads to a distorted result

Biologic marker (or biomarker)

a ...

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