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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.