Table 7

Simulation Results (Normal Distribution, 2:1 Experimental to Control Group Sizes, Standard Deviation 40% of Control Mean Value).

% Bias

% Coverage

% Statistical Power

I2(%)





τ = 0s

τ = 0.5s

τ = 0s

τ = 0.5s

τ = 0s

τ 0.5s

τ 0.5s








Δ

n (exp/contr)

k

MD

SMD

RoM

MD

SMD

RoM

MD

SMD

RoM

MD

SMD

RoM

MD

SMD

RoM

MD

SMD

RoM

MD

SMD

RoM


SMD = 0.2

14/6

5

-1

-5

0

0

-5

0

94

97

94

90

92

90

15

10

11

14

12

12

59

44

54

10

1

-4

-1

2

-4

-1

94

97

93

92

93

91

25

18

18

18

16

14

60

44

55

30

0

-5

-1

1

-6

-1

94

97

91

93

94

93

59

53

44

36

35

27

60

44

55


MD = 8

134/66

5

0

0

0

0

-1

0

96

97

97

88

88

88

78

77

76

21

21

21

92

91

91

RoM = 1.08

10

0

0

0

0

-1

0

96

96

96

92

91

91

98

98

97

27

27

27

92

91

91

30

0

0

0

0

-1

0

96

96

96

94

94

94

100

100

100

56

57

57

92

91

91



SMD = 0.5

14/6

5

0

-4

-1

0

-5

0

94

97

94

90

92

90

57

50

50

41

37

36

59

44

54

10

0

-5

-1

1

-5

-1

94

97

93

92

93

91

86

83

79

62

61

56

60

44

55

30

0

-5

-1

0

-6

-1

94

96

91

93

93

92

100

100

100

96

97

94

60

43

56


MD = 20

134/66

5

0

0

0

0

-1

1

96

96

97

88

88

88

100

100

100

60

61

60

92

91

91

RoM = 1.2

10

0

0

0

0

-1

0

96

96

96

92

92

91

100

100

100

85

86

85

92

91

91

30

0

0

0

0

-1

0

96

96

95

94

94

94

100

100

100

100

100

100

92

91

91



SMD = 0.8

14/6

5

0

-4

-1

0

-5

0

94

97

93

90

92

90

91

89

87

71

69

66

59

43

54

10

0

-5

-1

0

-5

-1

94

96

92

92

93

91

100

100

99

93

93

91

60

43

55

30

0

-5

-2

0

-6

-1

94

94

90

93

92

92

100

100

100

100

100

100

60

42

56


MD = 32

134/66

5

0

0

0

0

-1

1

96

96

96

88

88

88

100

100

100

91

91

91

92

91

91

RoM = 1.32

10

0

0

0

0

-1

0

96

96

96

92

92

91

100

100

100

100

100

100

92

91

91

30

0

0

0

0

-1

0

96

96

95

94

94

93

100

100

100

100

100

100

92

91

91


Results of 10,000 simulations per scenario with a standard deviation equal to 40% of the control mean, for each combination of effect size (0.2, 0.5, and 0.8 standard deviation units), number of patients (14/6 and 134/66 experimental/control patients per trial), and number of trials (5, 10, and 30). The "% Bias" columns show the bias of each effect measure (MD, SMD, RoM) expressed as percentages of the expected values (negative sign denotes less than expected value), with and without heterogeneity. The "% coverage" columns show the percentage of cases that the true value falls within the 95% confidence interval of the simulated result, with and without heterogeneity. The "% statistical power" columns show the percentage of cases that the 95% confidence interval of the simulated result yields a significant treatment effect (i.e. excluding zero for MD and SMD, and one for RoM), with and without heterogeneity. The I2 column shows the degree of heterogeneity only for the scenarios in which heterogeneity was introduced. (For all the scenarios without heterogeneity, the ratio of Q/(k-1) was close to unity as expected, corresponding to I2 = 0 [data not shown].)

Abbreviations for Table and Legend: contr – control, exp – experimental, I2 I2 heterogeneity measure, k – number of trials in each meta-analysis, n – number of experimental or number of control patients per trial, Q – Cochran's Q statistic for heterogeneity, MD – mean difference, RoM – ratio of means, s – standard deviation units, SMD – standardized mean difference.

Friedrich et al. BMC Medical Research Methodology 2008 8:32   doi:10.1186/1471-2288-8-32

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