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Observational analytical studies, both
case-control and cohort are often used to evaluate a screening program. In case-control
design individuals with or without the disease are compared with respect to their past
exposure to screening. However, as with any case-control study, the definition and
selection of cases and controls are important for the validity of the findings. Using a
cohort design, a case-fatality rate of those who chose to be screened is compared with the
comparable rate among those whose diagnoses were symptom-related. This is the most
frequently used approach for the evaluation of a screening program but in interpreting the
results, the potential effects of self-selection of participants, lead time and length
bias must be taken in consideration. |