INTERIM ANALYSIS - THE ALPHA-SPENDING FUNCTION-APPROACH

interim analysis of accumulating data in a clinical trial is now an es tablished practice for ethical and scientific reasons. Repeatedly test ing interim data can inflate false positive error rates if not handled appropriately. Group sequential methods are a commonly used frequenti st approach to-control this error rate. Motivated by experience of cli nical trials, the alpha spending function is one way to implement grou p sequential boundaries that control the type I error rate while allow ing flexibility in how many interim analyses are to be conducted and a t what times. In this paper, we review the alpha spending function app roach, and detail its applicability to a variety of commonly used stat istical procedures, including survival and longitudinal methods.