Based on data published by Manchana , 21% of symptomatic pelvic organ prolapse patients fitted successfully with a pessary had vaginal erosion. Let us assume a 60% reduction from this estimate (21% to 8.4%) after using Estrace®. A two group χ2 test with a 0.05 two-sided significance level will have 80% power to detect the difference between a vaginal erosion rate for the placebo group = 0.21 and a vaginal erosion rate of the Estrace® group = 0.084 when the sample size in each group is 123.