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Table 2 Required total sample size

From: Procalcitonin guided antibiotic therapy and hospitalization in patients with lower respiratory tract infections: a prospective, multicenter, randomized controlled trial

True assumed failure rate in both arms Required total sample size
  Δ = 5%
Power 90% (80%)
Δ = 7.5%
Power 90% (80%)
Δ = 10%
Power 90% (80%)
10% 1278 (932) 578 (426) 330 (244)
15% 1792 (1302) 806 (588) 458 (334)
20% 2232 (1624) 1002 (730) 570 (418)
  1. Sample size calculation for the primary endpoint, i.e. required sample size to conclude at the one-sided 5%-level that the disease-specific failure rate in PCT-guided arm is at most Δ higher compared to management with enforced guidelines with a power of 80–90%.