ets exposure, lung cancer - Legacy Tobacco Documents Library

Epidemioloaie Methodoloay,
Fpi.demiology involves the study of the occurrence rate off
disease and its association wit2-h specific exposures and other
factors in popul .ation groups .
In the process of epidemiologic investigation, the
researcher classifies subjects in a study according to whether ~r
not they have a condition or disease of interest (for exaraple, ~
lung cancer) and according to whether or not they have been
exposed to a factor of interest (for example, ETS) . The result!G
of this classification are then expressed as an "odds ratio" o~
"relative risk", which reflects the occurrence rate of the
disease in the exposed individual relative to the occurrence raf e
of the disease in the nonexposed individual,
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The results of all biologic studies, be they experimental ~r
epidemiologic, are subject to considerable uncertainty, since
variability from subject to subject is an inherent characteristuc
of biologic processes . Furthermore, in epidemiologic studies, as
a practical matter, only a relatively small sample of a nuch ~
larger population can he studied directly . Thus, the
investigator must attempt to determine whether an observation z' ;&
a real one (valid and reproducible on re-examination) or one du~a
to chance variation (and not necessarily valid or reproducible)I,
In order to assist the researcher in this determination of
potential reproducibility, reliability and validity of the
observations made, statistical analysis must be employed .
Statistical analyses not only take into consideration the
magnitude of an association but also the biologic variability
a population relative to this association. , !
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Statistical methods in eoidemiology not only estimate odd3
raLios but also so-called 95%, confidence intervals of the
estir..ate of risk . The 95% confidence interval is an estiL .ate ~ f
the variability and is expressed as a range above and below the ;
"poinz estimate" odds ratio . The wider the interval, t :;a greal-.;-r
the variability . If the lower boundary of the 95,1 confidenc +e
interval exceeds unity (1 .0), the odds ratio is usually regard
as being statistically significant,
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a~~dds ratio [an~ 9^`= ~-
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http://legacy.library.ucsf.edu/tid/wyk81f00/pdf
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