Skip to main content
. 2017 Jul 13;358:j3064. doi: 10.1136/bmj.j3064

Table 1.

Trade-off between number of clusters and cluster size for the case study

No of clusters in each arm 80% power 90% power
Cluster size Total sample size Cluster size Total sample size
6 191 2292 NA NA
7 89 1246 1383 19 362
8 58 928 191 3056
9 43 774 103 1854
10 35 700 70 1400
11 29 638 54 1188
12 25 600 43 1032
13 22 572 36 936
14 19 532 31 868
15 17 510 28 840

Sample size needed to detect a difference between two proportions of 0.60 and 0.45 at two sided significance level of 5%, assuming normal approximations (formula in Appendix 1).

Assumes 228 in each arm needed for 90% power and 171 for 80% power.

ICC assumed to be 0.03.

Rounding has occurred at some levels.

NA=not achievable