Sample size calculation
The sample size calculation was based upon clinical hypotheses, with a noninferiority margin set at 1.35%, an anticipated failure rate of 0.5% in the control group, the 2-sided α risk set at 5% and β set at 20%. The cluster design effect was estimated 1.37. Assuming that 5% of patients would not be evaluable, with 18 EDs and 2 periods per ED, 1234 patients were needed.