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An Assessment of the NIH Women's Health Initiative (1993)

Chapter: Appendix J: NIH Power Calculations

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Suggested Citation:"Appendix J: NIH Power Calculations." Institute of Medicine. 1993. An Assessment of the NIH Women's Health Initiative. Washington, DC: The National Academies Press. doi: 10.17226/2271.
×

J

NIH Power Calculations 1

1

Reprinted with permission from the June 28, 1993 WHI Protocol, pages 77-83.

Suggested Citation:"Appendix J: NIH Power Calculations." Institute of Medicine. 1993. An Assessment of the NIH Women's Health Initiative. Washington, DC: The National Academies Press. doi: 10.17226/2271.
×

(i) ERT versus Control: Coronary Heart Disease.

 

Power (%)

 

Percentage cases

Total sample size

Average follow-up (y)

Intervention effect (%)

Control

ERT (or PERT)

20,000

25,000

30,000

6

25

3.26

2.71

50

59

67

30

3.26

2.62

66

76

83

35

3.25

2.49

80

88

93

9

25

5.03

4.16

69

79

86

30

5.02

3.97

85

92

96

35

5.01

3.79

94

98

99

(ia) PERT versus Control: Coronary Heart Disease.

 

Power (%)

 

Percentage cases

Total sample size

Average follow-up (y)

Intervention effect (%)

Control

PERT

20,000

25,000

30,000

6

25

3.26

2.71

48

57

65

30

3.26

2.60

64

74

82

35

3.25

2.49

79

87

92

9

25

5.03

4.16

67

77

84

30

5.02

3.97

84

91

95

35

5.01

3.79

94

97

99

(ii) ERT versus Control: Combined Fractures.

(The percentage of cases and the powers in this table are based upon our original age distribution assumptions, i.e., 50-59, 60-69, 70-79 year olds enter in the ratio 2:2:1, and hence are conservative estimates.)

 

Power (%)

 

Percentage cases

Total sample size

Average follow-up (y)

Intervention effect (%)

Control

ERT

20,000

25,000

30,000

6

25

5.84

4.86

79

87

92

30

5.84

4.66

92

96

98

35

5.83

4.46

98

99

>99

9

25

8.85

7.31

94

97

99

30

8.84

6.99

99

>99

>99

35

8.82

6.66

>99

>99

>99

Suggested Citation:"Appendix J: NIH Power Calculations." Institute of Medicine. 1993. An Assessment of the NIH Women's Health Initiative. Washington, DC: The National Academies Press. doi: 10.17226/2271.
×

(iia) ERT versus Control: Combined Fractures.

(The percentage of cases and the powers in this table are based upon our original age distribution assumptions, i.e., 50-59, 60-69, 70-79 year olds enter in the ratio 2:2:1, and hence are conservative estimates.)

 

Power (%)

 

Percentage cases

Total sample size

Average follow-up (y)

Intervention effect (%)

Control

PERT

20,000

25,000

30,000

6

25

5.84

4.86

77

85

91

30

5.84

4.66

90

95

98

35

5.83

4.46

98

99

>99

9

25

8.85

7.31

93

97

99

30

8.84

6.99

99

>99

>99

35

8.82

6.66

>99

>99

>99

(iii) ERT versus Control: Hip Fractures.

 

Power (%)

 

Percentage cases

Total sample size

Average follow-up (y)

Intervention effect (%)

Control

ERT

20,000

25,000

30,000

6

25

2.34

1.94

41

49

56

30

2.34

1.86

55

65

73

35

2.33

1.77

70

79

86

9

25

3.91

3.22

62

71

79

30

3.90

3.07

78

87

92

35

3.89

2.92

90

95

98

(iiia) PERT versus Control: Hip Fractures.

 

Power (%)

 

Percentage cases

Total sample size

Average follow-up (y)

Intervention effect (%)

Control

PERT

20,000

25,000

30,000

6

25

2.34

1.94

39

47

54

30

2.34

1.86

54

63

71

35

2.33

1.77

68

77

84

9

25

3.91

3.22

60

69

77

30

3.90

3.07

76

85

91

35

3.89

2.92

88

94

97

Suggested Citation:"Appendix J: NIH Power Calculations." Institute of Medicine. 1993. An Assessment of the NIH Women's Health Initiative. Washington, DC: The National Academies Press. doi: 10.17226/2271.
×

(iv) ERT versus Control: Breast Cancer.

 

Power (%)

 

Percentage Cases

Total Sample Size

Average follow-up (y)

Increase due to ERT (%)

Control

ERT

20,000

25,000

30,000

6

20

2.07

2.25

13

15

17

30

2.08

2.35

23

28

32

9

20

3.04

3.40

27

33

38

30

3.05

3.60

52

61

69

14

20

4.5

5.17

52

62

70

30

4.53

5.54

85

92

96

(iva) PERT versus Control: Breast Cancer.

 

Power (%)

 

Percentage Cases

Total Sample Size

Average follow-up (y)

Increase due to PERT (%)

Control

20,000

ERT

25,000

30,000

6

20

2.07

2.25

12

14

16

30

2.08

2.35

22

27

31

9

20

3.04

3.40

26

32

37

30

3.05

3.60

50

60

67

14

20

4.50

5.17

51

60

68

30

4.53

5.54

83

91

95

Suggested Citation:"Appendix J: NIH Power Calculations." Institute of Medicine. 1993. An Assessment of the NIH Women's Health Initiative. Washington, DC: The National Academies Press. doi: 10.17226/2271.
×

(i) Dietary Modification: Breast Cancer.

 

Power (%)

 

Percentage of cases

Sample size

Average follow-up (y)

Intervention effect (%)

Control

Intervention

42,000

48,000

54,000

6

11

2.05

1.89

25

28

31

12

2.05

1.87

32

35

39

14

2.05

1.85

39

44

48

9

11

2.92

2.61

58

63

69

12

2.92

2.57

70

75

80

14

2.92

2.52

81

86

89

(ii) Dietary Modification: Colorectal Cancer.

 

Power (%)

 

Percentage of cases

Sample size

Average follow-up (y)

Intervention effect (%)

Control

Intervention

42,000

48,000

54,000

6

18

1.07

0.93

33

37

41

20

1.07

0.92

40

45

49

22

1.07

0.91

47

52

57

9

18

1.61

1.32

77

83

87

20

1.61

1.29

86

90

93

22

1.60

1.25

92

95

97

(iii) Dietary Modification: Coronary Heart Disease.

 

Power (%)

 

Percentage of cases

Sample size

Average follow-up (y)

Intervention effect

Control

Intervention

42,000

48,000

54,000

6

11

3.04

2.72

48

53

58

12

3.03

2.67

58

64

69

14

3.02

2.63

68

74

79

9

11

4.62

4.15

62

67

72

12

4.60

4.08

72

78

83

14

4.58

4.00

82

86

90

Suggested Citation:"Appendix J: NIH Power Calculations." Institute of Medicine. 1993. An Assessment of the NIH Women's Health Initiative. Washington, DC: The National Academies Press. doi: 10.17226/2271.
×

(i) Calcium/Vitamin D versus Control: Hip Fractures

 

Power (%)

 

Percentage cases

Total sample size

Average Follow-up (y)

Intervention effect (%)

Control

ERT (or PERT)

20,000

25,000

30,000

5

25

1.88

1.58

53

67

78

 

30

1.88

1.51

69

83

91

 

35

1.88

1.45

83

93

97

8

25

3.35

2.76

81

92

97

 

30

3.34

2.64

93

98

>99

 

35

3.34

2.51

98

>99

>99

(ii) Calcium/Vitamin D versus Control: Combined Fractures

(The percentages of cases and powers in this table are based upon our original age distribution assumptions i.e., 50-59, 60-69, 70-79 year olds enter in the ratio 2.2.1 and hence are conservative estimates.)

 

Power (%)

 

Percentage cases

Total sample size

Average Follow-up (y)

Intervention effect (%)

Control

Calcium/ Vitamin D

25,000

35,000

45,000

5

25

4.84

4.07

90

97

99

 

30

4.84

3.91

98

>99

>99

 

35

4.83

3.75

>99

>99

>99

8

25

7.85

6.49

99

>99

>99

 

30

7.83

6.20

>99

>99

>99

 

35

7.82

5.91

>99

>99

>99

(iii) Calcium/Vitamin D versus Control: Colorectal Cancer

 

Power (%)

 

Percentage cases

Total sample size

Average Follow-up (y)

Intervention effect (%)

Control

Calcium/ Vitamin D

25,000

35,000

45,000

5

18

0.86

0.76

17

23

28

 

20

0.86

0.75

20

27

33

 

22

0.86

0.74

24

31

38

8

25

1.42

1.17

52

66

77

 

30

1.42

1.15

60

75

85

 

35

1.42

1.12

69

83

91

Suggested Citation:"Appendix J: NIH Power Calculations." Institute of Medicine. 1993. An Assessment of the NIH Women's Health Initiative. Washington, DC: The National Academies Press. doi: 10.17226/2271.
×
Page 127
Suggested Citation:"Appendix J: NIH Power Calculations." Institute of Medicine. 1993. An Assessment of the NIH Women's Health Initiative. Washington, DC: The National Academies Press. doi: 10.17226/2271.
×
Page 128
Suggested Citation:"Appendix J: NIH Power Calculations." Institute of Medicine. 1993. An Assessment of the NIH Women's Health Initiative. Washington, DC: The National Academies Press. doi: 10.17226/2271.
×
Page 129
Suggested Citation:"Appendix J: NIH Power Calculations." Institute of Medicine. 1993. An Assessment of the NIH Women's Health Initiative. Washington, DC: The National Academies Press. doi: 10.17226/2271.
×
Page 130
Suggested Citation:"Appendix J: NIH Power Calculations." Institute of Medicine. 1993. An Assessment of the NIH Women's Health Initiative. Washington, DC: The National Academies Press. doi: 10.17226/2271.
×
Page 131
Suggested Citation:"Appendix J: NIH Power Calculations." Institute of Medicine. 1993. An Assessment of the NIH Women's Health Initiative. Washington, DC: The National Academies Press. doi: 10.17226/2271.
×
Page 132
Next: Appendix K: Women's Health Initiative Clinical Coordinating Center and Vanguard Clinical Centers Principal Investigators »
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The National Institutes of Health Women's Health Initiative (WHI) is the largest research study ever funded by NIH ($625 million over 14 years) and is designed to test strategies to prevent cardiovascular disease, breast cancer, and osteoporotic fractures—leading causes of death, disability, and decreased quality of life for older women. Although the WHI has already begun, serious questions remain about its design, cost, and the likelihood that it can answer the questions it asks. This book evaluates whether the effort can be justified scientifically.

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