Accuracy: 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.
Acute: a disease of short duration.
Acute myelogenous leukemia (AML): a
heterogeneous group of disorders, also known as acute nonlymphocytic
leukemia, each of which involves the uncontrolled proliferation
of primitive blood-forming cells.
Adjustment: a procedure for overall
comparison of two or more populations in which background differences in
the distribution of covariables are removed. (See also Standardization.)
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 (eg, the population of the United States in 1940).
Allele: an alternate form of a
gene or a genetic locus that differs from other forms in its specific
sequence of nucleotides; certain alleles may affect the structure
and function of the corresponding protein coded for by that gene,
in turn affecting the susceptibility to a particular condition.
Alpha error: see Type I error.
Alzheimer’s disease: the
most common form of dementia in many populations, first described
in 1907 by Alois Alzheimer; affected individuals have characteristic
abnormalities in their brains, including neurofibrillary tangles
and plaques with a protein fragment, β-amyloid, at their core.
Analytic epidemiology: activities
related to the identification of possible determinants of disease
Analytic study: a research investigation
designed to test a hypothesis, often used in reference to a study
of an exposure–disease association.
Anthrax: an infectious disease
caused by a spore-forming bacterium Bacillus
anthracis. The natural occurrence of this illness typically
involves inhalation of spores from animal products. This agent was
used as a weapon of bioterror in 2001 in the United States, resulting
in 22 cases and 5 deaths.
Antibody: 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.
Antigen: a protein, usually foreign
in origin, that is capable of generating an immune response in a
Antigenic drift: mutation of a
pathogen (eg, ...