Click on image to view larger version.

Figure 1 Estimation of the non-inferiority margin for Stroke Prevention Using Oral Thrombin Inhibitor in Atrial Fibrillation (SPORTIF) trial. Individual data for the six historical studies of warfarin versus placebo are shown above the dashed line. Summary effects and estimation of non-inferiority margin are shown below the dashed line for all six trials (n = 6) and five primary prevention (PP) (minus European Atrial Fibrillation Trial [EAFT]) trials (n = 5). Summary effects were calculated with pooled analysis derived by adding all the events together, Mantel Haenszel method for fixed-effect meta-analysis (MA), and DerSimonian-Laird method for random-effect MA. The margin is typically estimated as 50% of the 95% lower limit of the absolute risk difference (ARD) derived from a random-effects MA (e.g., 50% of 1.36% = 0.68%). The corresponding risk ratio (RR) margins are on the basis of an assumed warfarin event rate of 3.1% (e.g., ARD of 0.68 = RR 1.22 [(3.1 + 0.68)/3.1 = 3.78/3.1]). AFASAK = Atrial Fibrillation, Aspirin and Anticoagulation; BAATAF = Boston Area Anticoagulation Trial for Atrial Fibrillation; CAFA = Canadian Atrial Fibrillation Anticoagulation; DB = double-blind; OL = open-label; SP = secondary prevention; SPAF I = Stroke Prevention in Atrial Fibrillation I; SPINAF = Stroke Prevention in Non-Rheumatic Atrial Fibrillation.