FAQ/PRsq

The table below gives the total sample size required for 90% and 80% power for upto 8 groups in a one-way anova. In each case the type I error is taken as 5%. The rows in bold correspond to Cohen's rules of thumb for small, medium and large effect sizes.

	90% power						80% power
R-squared	K=3	K=4	K=5	K=6	K=7	K=8	K=3	K=4	K=5	K=6	K=7	K=8
0.010	1269	1424	1550	1656	1750	1840	969	1096	1200	1290	1372	1448
0.059	207	232	255	270	287	304	159	180	200	216	231	240
0.10	117	132	144	154	163	172	90	103	113	122	130	137
0.138	84	96	105	114	119	128	66	76	80	90	98	104
0.15	76	85	93	100	106	111	58	66	73	79	84	89
0.20	54	61	67	72	77	81	42	49	54	58	62	65
0.25	42	47	52	56	59	63	33	38	42	45	48	51
0.30	33	38	42	45	48	51	27	30	34	37	39	42
0.35	28	31	34	37	40	42	22	25	28	31	33	35
0.40	23	27	29	32	34	36	19	22	24	26	28	30
0.45	20	23	25	27	29	31	16	19	21	23	25	27
0.50	17	20	22	24	26	27	14	16	18	20	22	23
0.55	15	17	19	21	23	24	12	15	16	18	20	21
0.60	13	15	17	19	20	22	11	13	15	16	18	19

Sample sizes for selected values of R-squared and different numbers of groups in a one-way anova