Table 1. Total required sample size for a 1:1 randomized trial designed to demonstrate superiority of IVIg compared with placebo at the 2-sided 5% significance level with 90% power*.

Absolute risk of progression, IVIg group	Absolute risk increase for placebo group compared with IVIg
	+5%	+7.5%	+10%	+15%
15%	2,424	1,136	670	322
20%	2,928	1,350	784	370

*Sample sizes are total sample sizes (i.e., for both groups combined) but do not account for loss-to-follow-up or increases in sample size that would be required if formal interim analyses with stopping boundaries are planned. IVIg, intravenous immunoglobulin.