A review of nonparametric tests for changepoint problems, with application to a recombinant drug therapy clinical trial.

We review general classes of nonparametric tests for the changepoint problem. We extend these tests to analyze the results of a clinical trial examining whether pretreatment of surgical patients with erythropoietin reduces their subsequent need for blood transfusions. We find a changepoint in baseline hemoglobin levels, below which pretreatment with erythropoietin appears particularly beneficial relative to placebo.