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without the disease. The relation of an attribute (e.g.,
immunization) to the disease is examined by comparing the diseased
and nondiseased groups with regard to how frequently the attribute
is present, or if quantitative, the levels of the attribute, in
each of the groups.
Cohort study. (Syn: prospective, follow-up study). A
study in which subsets of a defined population can be identified
who are, have been, or in the future may be exposed or not exposed,
or exposed in different degrees, to a factor or factors
hypothesized to influence the probability of occurrence of a given
disease (adverse event) or other outcome. The essential feature of
the cohort design is observation of the population for a sufficient
length of time to generate reliable incidence or mortality
Controlled study. Controlled studies are studies that use
a comparison group that differs from the subjects of the study in
either disease experience (outcome) or allocation to a regimen
(exposure). Allocation to a regimen can be random, as in a
randomized clinical trial or study, or nonrandom, as in an
observational cohort study or a case-control study.
DPT vaccine. See Vaccine, DPT v.
DTP vaccine. See Vaccine, DTP v.
Encephalopathy. Refers to a variety of conditions
affecting the brain resulting in alterations in the level of
consciousness, ranging from stupor to coma. At times, febrile
seizures, afebrile seizures, and epilepsy have been considered
components of encephalopathy (see Chapter 4).
Erythema multiforme. An inflammatory eruption
characterized by symmetrical erythematous, edematous, or bullous
lesions of the skin or mucous membranes.
Experimental study. A study in which a population is
selected for a planned trial of a regimen (e.g, immunization) whose
effects are measured by comparing the outcome of the regimen in the
experimental group with the outcome of another regimen in a control
group. Allocation of individuals to experimental or control groups
is ideally by randomization.
Guillain-Barrè syndrome. An acute, usually rapidly
progressive form of polyneuropathy characterized by muscular
weakness and mild distal sensory loss.
Hemolytic anemia. Anemia caused by lysis of red blood
cells, which leads