Table 2.

Minimum total sample size based on the number of time points, the expected marginal probabilities of the outcome, and the within-subject covariance structure and correlation ^a

Number of time points	Probabilities		Compound symmetry (CS) within-subject covariance structure and correlation			First-order autocorrelation (AR(1)) within-subject covariance structure and correlation
	p1	p2	ρ = 0.2	ρ = 0.5	ρ = 0.8	ρ = 0.2	ρ = 0.5	ρ = 0.8
T = 3	0.1	0.2	152	214	276	140	192	260
		0.3	52	74	94	48	66	88
		0.4	30	42	52	28	38	50
		0.5	22	28	36	20	26	34
	0.2	0.3	224	314	402	206	282	380
		0.4	68	92	118	62	84	112
		0.5	34	48	60	32	42	56
	0.3	0.4	280	386	492	254	348	466
		0.5	76	106	134	70	96	126
	0.4	0.5	308	424	540	280	382	512
T = 6	0.1	0.2	110	188	264	76	122	206
		0.3	40	64	90	28	42	70
		0.4	24	38	52	16	26	40
		0.5	22	26	34	12	18	28
	0.2	0.3	166	276	386	114	180	302
		0.4	50	82	114	34	54	88
		0.5	26	42	58	18	28	46
	0.3	0.4	208	342	474	140	222	370
		0.5	58	94	130	40	62	102
	0.4	0.5	230	376	520	156	244	406

^aEstimates are for the minimum total sample required in two groups, with a sample allocation ratio of 1:1, for comparison of event probabilities p₁ and p₁ assumed to be constant over time, with use of the logit link for various values T, p₁, p₁, and ρ. Estimates shown are for setting the random effects to G = 1, type I error to 0.05, and type II error to 0.20.