3.6 SAMPLE SIZE Recent studies had determined the 42-day risk of recurrent parasitaemia due to recrudenscence (treatment failure) in children to range from 0.9-6% with Coartem® therapy14;17;21;22. Therefore on the basis of a conservative estimated risk of recurrent parasitaemia (due to recrudescence, PCR corrected) of 5%, we calculated that 120 patients per treatment arm would be needed to detect a difference in the risk of recurrent parasitaemia between treatment arms of no greater than 7% (one-sided type I error of 5%, 80% power)23.