Table 2:

Total sample sizes necessary to yield 80% or 90% power to detect a treatment-by-subgroup interaction in crossover studies.

80% Power
SES	Subgroup Allocation
	50:50					34:66					25:75
	Correlation†
	0.8	0.6	0.5	0.4	0.2	0.8	0.6	0.5	0.4	0.2	0.8	0.6	0.5	0.4	0.2
	Sample Size
1.0	15	27	34	39	54	17	31	37	44	58	19	35	44	53	70
0.9	18	34	42	50	64	20	37	46	55	72	22	43	54	64	86
0.8	22	42	51	62	82	26	46	58	68	90	29	54	67	82	107
0.7	27	54	67	79	106	31	60	74	88	117	37	70	87	106	139
0.6	38	71	90	107	142	41	80	99	120	158	50	94	118	142	188
0.5	54	103	127	154	203	58	114	143	170	226	70	136	171	203	270
0.4	82	159	199	238	315	90	178	221	264	352	107	211	263	316	422
0.3	142	282	351	422	562	158	314	390	469	624	188	374	467	561	747
90% Power
SES	Subgroup Allocation
	50:50					34:66					25:75
	Correlation†
	0.8	0.6	0.5	0.4	0.2	0.8	0.6	0.5	0.4	0.2	0.8	0.6	0.5	0.4	0.2
	Sample Size
1.0	19	35	45	54	70	22	40	49	58	78	26	46	59	70	91
0.9	23	43	54	66	86	26	49	61	73	95	30	59	70	86	114
0.8	30	55	67	82	107	31	61	75	90	120	38	73	91	107	142
0.7	38	71	87	106	139	40	78	98	117	155	48	94	117	139	187
0.6	50	95	119	143	190	55	107	132	158	211	65	126	158	190	251
0.5	70	138	171	203	271	78	152	190	227	302	91	182	227	270	362
0.4	107	214	266	318	423	120	237	296	354	470	142	283	353	422	563
0.3	190	375	470	563	750	211	419	523	627	834	251	501	626	750	998

SES = Difference in standardized effect size between subgroups

^†Correlation between the within-subject outcomes (treatment and placebo conditions)