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A
number of epidemiologic designs are utilized to evaluate screening programs,
including correlation studies, observational analytical studies and
randomized trials. Correlation studies have been used to examine disease
trends in relation to screening frequencies within a population or to
compare the relationship between the frequencies of screening and disease
rates for different populations. Correlation studies are useful in
suggesting a relationship between screening and decline in morbidity or
mortality. However, since the information from these studies concerns
populations rather than individuals, it is not possible to identify that
those experiencing the benefit are the same persons who received screening.
Also, such studies cannot allow for control of potential confounding risk
factors. Finally the measure of screening frequency is usually an average
value for the population, so it is impossible to determine an optimal
screening strategy for an individual.
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