When more than one response is of primary interest in a clinical trial, use of univariate stopping rules for allowing interim analyses is inappropriate. This paper considers the case where two endpoints are of interest and presents general methodology for the design, monitoring, and analysis of such trials. Two examples are presented of situations in which the technique could be implemented; the first is a trial in Alzheimer's patients, the second concerns women with osteoporosis. The appropriate application of the procedure can lead to the same ethical and economic benefits of univariate sequential designs, and so carries the potential to lead to more efficient clinical trials.
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