Continuous and Binary Endpoints

Outcomes are either continuous or dichotomous. Primary and secondary outcomes must be defined a priori in the protocol. The sample size for the study is based on the primary outcome.

When determining  if a clinical trial is effective we test a hypothesis of a primary outcome, and we may have several secondary outcomes which are more exploratory. We can't define many outcomes and pick the most successful, it would be like rolling dice many times; It increases the chance of type 1 error (rejecting the null hypothesis when it is true). One could also adjust the p-value/type one error rate to account for multiple testing, but more on this later.

When relevant to the study continuous variable can be coded as a binary one, but leads to a loss of information.