Cross-sectional and cohort studies are important epidemiological study designs in oncology. In cross-sectional studies, information on exposure is collected at the same time as information on outcome. In oncology these studies are mainly performed to measure the prevalence of an outcome. There is no follow-up period for the study participants; thus we cannot establish the causality or association between exposure and the subsequent development of the disease under investigation, because we cannot determine what has occurred first (exposure-disease/cause-effect). These studies generate hypotheses for further investigation.
Cohort studies, on the other hand, are studies in which, from a potential baseline cause (exposure) one investigates its effect (outcome). Therefore, these studies represent a very good design for evaluating causality. They can be prospective or retrospective, and the study population is divided into subgroups according to exposure characteristics (exposed and not-exposed). The study then assesses outcome after a given period of time, allowing the measurement of association (relative risk) for the outcome to be observed in the exposed and the not-exposed individuals. In oncology, cohort studies are mostly used to study risk factors or prognostic factors.
Cross-sectional study Cohort study Exposure Outcome Risk factors Prognostic factors
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