Table 2.

Total sample sizes (averaged over 100 simulated pairs of data sets) required for 80% power to detect specified effect sizes in a 1:1 two-arm clinical trial (ρ = r = 0.5). weights estimated from training data set with 40 subjects; mean and SD on the combined outcome estimated from either the same data set or another independent sample of the same size. Efficacy comparison assumed at time=3. N_i =total sample size using i-th efficacy outcome alone; N =total sample size using the true weight for the combined outcome; NP =total sample size using the combined outcome with weights estimated from training data sets and mean/SD estimated from validation data sets; NS = total sample size using the combined outcome with weights and SD estimated from the same data sets. ES=effect size as a percentage of improvement from the estimated mean for the placebo at t=3)

ES	N1	N2	N3	N	NP	NS	NP – NS
20%	837	711	564	370	384	342	42
25%	536	456	362	237	246	220	27
30%	373	317	251	165	171	153	19
35%	274	233	185	121	126	112	14
40%	210	179	142	93	97	86	11
45%	166	141	112	74	77	68	9
50%	135	115	91	60	62	56	7