A study is suggested in which Atrial Fibrillation patients a

A study is suggested in which Atrial Fibrillation patients are randomly divided into two groups: one receives the anticoagulant Warfarin, the other a placebo. The groups are to be followed to determine the incidence of embolic stroke. Suppose that 6% of treated patients and 22% of control patients are anticipated to experience embolic stroke over 3 years. How large a sample will be needed to compare the three year stroke rate between the two groups with 90% power ?

Hint: to compare two proportions using independent samples with n1 = n2 = n we set n = multiplier / E2. Use radians when computing E as follows:

E = square root 2 [arcsine (square root p1) -arcsine (square root p2)]

Solution