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Table 3 Design effects calculations for three different group distributions among centers.

From: Design effect in multicenter studies: gain or loss of power?

Group distribution among centers Quite homogeneous Heterogeneous Cluster design
Group size per center m 1j m 2j %* m 1j m 2j %* m 1j m 2j %*
Center 1 (n = 57) 16 41 28 11 46 19 0 57 0
Center 2 (n = 38) 10 28 26 24 14 63 38 0 100
Center 3 (n = 44) 11 33 25 7 37 16 0 44 0
Center 4 (n = 15) 3 12 20 1 14 7 0 15 0
Center 5 (n = 41) 9 32 22 8 33 20 0 41 0
Center 6 (n = 19) 5 14 26 10 9 53 19 0 100
Center 7 (n = 37) 8 29 22 9 28 24 0 37 0
Center 8 (n = 52) 12 40 23 4 48 8 0 52 0
Center 9 (n = 12) 3 9 25 1 11 8 0 12 0
Center 10 (n = 28) 8 20 29 10 18 36 28 0 100
S 0.14 5.79 33.77
Deff ( ρ = 0.10) 0.91 1.48 4.28
  1. *group 1 proportion in each center
  2. The global proportion of subjects in group 1 is 25%, for each group distribution, and the Intraclass Correlation Coefficient is equal to 0.10.