A clinical trial where at least one test treatment and one control treatment, often placebo, are randomly allocated to patients.
Cohorts are defined populations. A Cohort Study is an observational study in which a defined population is followed over a period of time. The outcomes of people in different subsets of the cohort are compared, to examine exposures to a particular factor of interest or an intervention. Cohort studies can be either prospective or retrospective.
A study that compares people with a specific disease or outcome of interest to people from the same population without the disease or outcome (Controls). The study then tries to find links between the outcome and prior exposure to particular risk factors. Case-control studies are usually retrospective.
Studies in which the presence or absence of disease or other health-related variables are determined in each member of the study population or in a representative sample at one particular time.
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