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ity, and impulsivity. Many children with ADD also exhibit symptoms of a learning disability, and many children with reading disabilities also exhibit evidence of ADD.

Attributable fraction (exposed). The attributable fraction among exposed individuals is the proportion by which the incidence rate of the outcome among those exposed would be reduced if the exposure were eliminated. It is assumed that causes other than the one under investigation have had equal effects on exposed and unexposed groups and that the effects of exposures are additive.

Attributable fraction (population). The attributable fraction in the population is the proportion by which the incidence rate of the outcome in the entire population would be reduced if the exposure were eliminated. It is assumed that causes other than the one under investigation have had equal effects on the exposed and unexposed groups and that the effects of exposure are additive.

Attributable risk (exposed). The rate of a disease or other outcome in exposed individuals that can be attributed to the exposure. This measure is estimated by subtracting the rate of the outcome (usually incidence or mortality) among unexposed individuals from the rate among exposed individuals. It is assumed that causes other than the one under investigation have had equal effects on exposed and unexposed groups and that the effects of different causes are additive. This term is often used, incorrectly, to denote the attributable fraction among exposed individuals and in the population.

Autism. The condition of being dominated by subjective, self-centered trends of thought or behavior that are not subject to correction by external information. One form, infantile autism, is a condition of the early years of life characterized by failure to relate in the usual way to people and situations and by repetitive activities, developmental language disorders, and a marked inability to adjust socially.

B

Bias. Deviation of results or inferences from the truth, or processes leading to such deviation.  Any trend in the collection, analysis, interpretation, publication, or review of data that can lead to conclusions that are systematically different from the truth. Not to be confused with prejudice or partisan point of view, as is the conventional usage.

C

Case-comparison study. (Syn: case-control study). A study that starts with the identification of persons with the disease or condition (adverse event) of interest and a suitable control (comparison) group of persons



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