Jose Carvalho, Statistician, Statistics Consultoria
Postpartum hemorrhage (PPH) is a major cause of maternal death in low-resource countries, accounting for 661,000 deaths worldwide between 2003 and 2009. To assess this burden, the WHO conducted studies to find methods for the prevention and treatment of PPH. Three large clinical trials were conducted in the past two decades by collecting blood loss volume data (V) for more than 70,000 deliveries. The outcomes were PPH (V> 500 mL) and severe PPH (V> 1000 mL). The parameters under comparison were the proportion of these events. The comparisons of small proportions led to very large (20,000 to 30,000) trial sizes.
By using data from large trials, the Survival platform in JMP Pro clearly showed that the distribution of V is very close to the lognormal distribution. This finding allowed the efficiency of estimates of probabilities and relative risks to be improved and permitted a substantial reduction of sample size for treatments comparison (typically less than 4,000), in view of those needed by the binomial outcome. Quicker and less expensive trials are very welcome to speed up obtaining results and have become common practice.
