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Often the main aim of a medical study is to estimate or test an unknown parameter of interest, such as the incidence of a certain disease, the effect of a certain treatment, or the relative risk associated with a certain exposure. An important issue in the design of a study is the choice of the number of subjects to include. The larger the study sample, the more precise a parameter estimate will be, and the choice of the sample size will depend on how much precision is required. If the aim of the study is to demonstrate that a certain treatment is effective, the power of the study is very important. The power is the chance that the study, through a statistically significant treatment effect, ...

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