Planning a cluster randomized trial with unequal cluster sizes: practical issues involving continuous outcomes

Table 4 Required sample size and empirical Type I error and power when using corrected variance inflation factors with an a priori hypothesized Pareto imbalance in cluster size – Effect size = 0.50

		No correction			Equal weights			Cluster size weights¹			Minimum variance weights
Intraclass correlation coefficient (ρ)	Number of clusters in each arm (g)	Sample size	Empirical probabilities		Sample size	Empirical probabilities		Sample size	Empirical probabilities		Sample size	Empirical probabilities
			Type I error	Power		Type I error	Power		Type I error	Power		Type I error	Power
0.005	5	89	0.0256	0.6250	288	0.0536	0.9330	111	0.0270	0.7156	108	0.0324	0.6906
	10	73	0.0352	0.7090	236	0.0528	0.9768	79	0.0306	0.7370	79	0.0306	0.7370
	20	67	0.0334	0.7322	218	0.0470	0.9912	70	0.0390	0.7524	70	0.0390	0.7524
	40	65	0.0382	0.7518	210	0.0394	0.9970	66	0.0400	0.7558	66	0.0400	0.7558
0.02	5	119	0.0674	0.6262	387	0.1072	0.8642	-	-	-	256	0.0954	0.7946
	10	81	0.0550	0.6910	261	0.0900	0.9346	127	0.0654	0.7990	115	0.0672	0.7856
	20	70	0.0460	0.7056	226	0.0684	0.9752	83	0.0492	0.7680	82	0.0482	0.7680
	40	66	0.0422	0.7328	212	0.0534	0.9908	71	0.0390	0.7540	71	0.0390	0.7540
0.05	5	423	0.0768	0.6808	1375	0.0578	0.8130	-	-	-	1311	0.0556	0.7962
	10	103	0.0770	0.6342	335	0.0824	0.8600	-	-	-	230	0.0920	0.7952
	20	76	0.0528	0.6620	245	0.0652	0.9284	136	0.0706	0.8252	115	0.0628	0.7872
	40	67	0.0516	0.7026	217	0.0590	0.9712	83	0.0578	0.7694	81	0.0488	0.7772
0.15	10	213	0.0730	0.6394	691	0.0548	0.8042	-	-	-	631	0.0572	0.8002
	20	89	0.0674	0.6276	290	0.0644	0.8646	-	-	-	193	0.0638	0.7888
	40	70	0.0536	0.6641	225	0.0564	0.9316	122	0.0506	0.8208	104	0.0578	0.7838

ISSN: 1471-2288