. Author manuscript; available in PMC: 2010 Mar 29.

Published in final edited form as: J Neurol Neurosurg Psychiatry. 2009 Feb 9;80(11):1218–1223. doi: 10.1136/jnnp.2008.154732

Table 3.

Sample size required to detect the specified reduction in the per cent change estimated from each dataset (table 2) based on a 2 year study with a baseline, year 1 and year 2 scan

Dataset	Measurement	33% reduction	50% reduction	90% reduction
RRMS₁	GMV	328	147	46
	WMV	3859	1712	527
	BPV	603	269	84
RRMS₂	GMV	1127	503	157
	WMV	18944	8425	2605
	BPV	724	323	100
RRMS₃	GMV	419	187	59
	WMV	1414	627	193
	BPV	2391	1064	329

Each sample size calculation assumes a 1:1 allocation of patients to treatment and placebo, 80% power and a two sided significance level of 0.05. Sample sizes are totals for both arms.

BPV, brain parenchymal volume; GMV, gray matter volume; RRMS, relapsing–remitting multiple sclerosis; RRMS1, untreated cohort of RRMS patients observed monthly for 9 months¹⁴; RRMS2, untreated cohort of RRMS patients observed every 3 months for 1.5 years¹⁷; RRMS₃, treated cohort of RRMS patients observed monthly for 9 months¹⁴; WMV, white matter volume.