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Controlled Study

A study that compares a group with an exposure or outcome of interest with a group that does not have the exposure or outcome. When study subjects are randomly assigned to exposed or unexposed groups by the study researcher (e.g., are assigned to receive or not receive a vaccine or drug) and subsequent differences in outcomes measured, the study is called a randomized clinical trial. Studies in which exposure status is not controlled by researchers are called ‘observational’ and include cohort and case-control studies.