Exact sequential tests for single samples of discrete responses using spending functions

Sequential tests are increasingly used to reduce the expected sample size of trials in medical research. The majority of such methods are based on the assumption of normality for test statistics. In clinical trials yielding a single sample of discrete data, that assumption is often poorly satisfied. In this paper we show how a novel application of the spending function approach of Lan and DeMets can be used together with exact calculation methods to design sequential procedures for a single sample of discrete random variables without the assumption of normality. A special case is that of binomial data and the paper is illustrated by the design of a cytogenetic study which motivated this work.