Table 3. Sample Size Estimates.

Iodine risk ratio	Iodine odds ratio	Sample size	Sample size increased by 10%
Aqueous-PREP and the PREPARE open fracture cohorta
10.0% Baseline SSI risk
0.62	0.59	1600	1760
0.65	0.63	1960	2100
0.67	0.65	2200	2420
0.70	0.68	2600	2860
12.5% Baseline SSI risk
0.62	0.59	1300	1440
0.65	0.62	1400	1540
0.67	0.64	1600	1760
0.70	0.67	1800	1980
14.0% Baseline SSI risk
0.62	0.58	1200	1320
0.65	0.61	1300	1440
0.67	0.64	1500	1660
0.70	0.67	1800	1980
PREPARE closed fracture cohorta
2.0% Baseline SSI risk
0.62	0.62	8200	9020
0.65	0.65	10 000	11 000
0.67	0.67	11 400	12 540
3.5% Baseline SSI risk
0.62	0.61	4700	5170
0.65	0.64	5700	6280
0.67	0.66	6600	7260
5.0% Baseline SSI risk
0.62	0.61	3300	3640
0.65	0.64	4100	4520
0.67	0.67	4300	4740

Abbreviations: Aqueous-PREP, Pragmatic Randomized Trial Evaluating Pre-Operative Aqueous and Antiseptic Skin Solution in Open Fractures; PREPARE, Pragmatic Randomized Trial Evaluating Pre-Operative Alcohol Skin Solutions in Fractured Extremities; SSI, surgical site infection.

^aInitial assumptions for sample size estimates: between-cluster intraclass correlation coefficient = 0.028; between-cluster variance = 0.095; between-period variance = 0; 10 clusters; 2 periods; α = .05.