Rationale and design of the PeriOperative ISchemic Evaluation-3 (POISE-3): a randomized controlled trial evaluating tranexamic acid and a strategy to minimize hypotension in noncardiac surgery

Table 3 Sample size calculation for non-inferiority safety hypothesis of tranexamic acid vs. placebo

Placebo event rate	NI margin, absolute risk difference TXA vs. placebo^b	Power	Sample size^c
		0.90	8,868
10%^a	1.18%	0.95	10,963
		0.97	12,441
		0.90	8,078
11%^a	1.29%	0.95	9,990
		0.97	11,340
		0.90	7,390
12%^a	1.39%	0.95	9,136
		0.97	10,367

NI non-inferiority margin, TXA tranexamic acid
^aThe estimates are based on the event rates observed in the POISE-2 trial (aspirin-placebo group) [5] and in a simulated subpopulation of the VISION cohort [1, 2] matching the POISE-3 inclusion criteria
^bThese are the NI margins expressed as absolute risk differences, corresponding to a NI margin expressed as hazard ratio of 1.125, when the placebo event rate is 10%, 11%, or 12%
^cThese sample sizes are obtained from non-inferiority test for two survival curves using Cox’s proportional hazard model, with a hazard ratio of 1.125 as non-inferiority margin, and a hazard ratio of 0.9 as actual hazard ratio (one-sided test, alpha of 0.025)

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