ABSTRACT
Despite a great effort, we often face a high degree of uncertainty about param-
eters when designing a trial or justifying the sample-size at the design stage.
This could involve the initial estimates of treatment effect and variability.
When the uncertainty is greater, a classical design with a fixed sample-size is
inappropriate. Instead, it is desirable to have a trial design that allows for
reestimation of sample-size at the interim analysis. Several different methods
have been proposed for sample-size reestimation (SSR), including the blinded,
unblinded, and mixed methods.
