Table 3

Numbers of patients/arm needed to perform PGB trials with statistical powers of 80% or 90% to detect treatment effects ranging from 50% to 80%

Treatment effects		No of scans		Statistical powers
				80%				90%
				Group A	Group B			Group C	Group A	Group B	Group C
50%	3	57	43	65		80	65	85
	6	50	38	62		70	55	80

60%	3	42	32	48		58	45	62
	6	38	25	42		50	36	57

70%	3	34	26	40		47	38	52
	6	29	22	36		38	32	46

80%	3	25	19	30		35	28	40
	6	22	18	27		30	25	38

Group A: patients with RRMS not selected for MRI activity at entry;
Group B: patients with RRMS selected for MRI activity at entry;
Group C: patients with SPMS not selected for MRI activity at entry.
For further details and statistical analysis: see the text.