title: p-value and power computations in multiple look trials.
abstract: This paper presents at an instructive level detailed design, decision and computational aspects of p-values and power for clinical trials in which interim looks at accumulating data are planned. Background theory and an application are presented. In addition, a definition of the term p-value, appropriate for a trial in which interim looks are planned is proposed. The definition is intuitively consistent with that for a fixed sample size trial. That is, the p-value reflects the strength of the data against the null hypothesis. For trials incorporating group sequential methods, the p-value at a particular look reflects the conditional nature of the data collected through that look on the data collected through earlier looks.
mesh_terms: D002986:Clinical Trials as Topic; D006801:Humans; D011336:Probability; D012107:Research Design; D012494:Sampling Studies; D013223:Statistics as Topic / Q000379:methods