Principles of Sample Size Calculation

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5. What Drives a Sample Size Calculation?

5.2. The Choice of the Primary Endpoint(s)

Endpoints in clinical research are the outcomes measured during the study that are used to assess the efficacy of the treatment. They can be of different types:

  1. Binary vs. continuous: binary indicates whether an event has occurred (occurrence or relief of symptoms), while continuous represents a specific measure or count (e.g., blood pressure).

  2. Landmark: its goal is to have a fixed time (time-to-event) after the initiation of the treatment, where analysis of survival can be conducted.
The type of endpoint (continuous, binary or time-to-event) can have a major impact on the size of a trial. Moreover, the sample size will have to be increased in case of multiple endpoints. The significance level may have to be adapted for limiting the overall type I error rate.