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Table 2 interim analyses and potential recommendations of the DSMB to stop the trial for futility or efficacy, depending on the observed treatment effect (and associated P-value)

From: A multicenter randomized trial to assess the efficacy of CONvalescent plasma therapy in patients with Invasive COVID-19 and acute respiratory failure treated with mechanical ventilation: the CONFIDENT trial protocol

Interim analysis Number of patients Recommend stopping for futility if difference in mortality is smaller than Recommend stopping for efficacy if difference in mortality is greater than
1 100 0.02 (P > 0.83) -
2 200 0.04 (P > 0.60) 0.22 (P < 0.001)
3 300 0.06 (P > 0.28) 0.14 (P < 0.007)
4 400 0.08 (P > 0.12) 0.11 (P < 0.022)
5 (final) 500 - 0.09 (P < 0.042)