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Table 1 Standard deviation and required sample size (percent reduction) as a function of 1–5 measurements

From: Two to five repeated measurements per patient reduced the required sample size considerably in a randomized clinical trial for patients with inflammatory rheumatic diseases

Standard deviation

Variable

1 measure

2 measures

3 measures

4 measures

5 measures

GHQ

8.44

7.51

7.01

6.76

6.39

Pain

2.11

1.97

1.95

1.92

1.86

Fatigue

2.47

2.22

2.12

2.13

2.15

Disease activity

1.89

1.80

1.79

1.77

1.73

Self-care

1.92

1.77

1.67

1.69

1.69

Emotional well-being

1.73

1.65

1.52

1.47

1.43

Required sample size (percent reduction) per group

Variable

1 measure

2 measures

3 measures

4 measures

5 measures

GHQ

56

44 (21)

39 (30)

36 (36)

32 (43)

Pain

71

61 (14)

60 (15)

58 (18)

55 (23)

Fatigue

96

78 (19)

71 (26)

72 (25)

73 (24)

Disease activity

57

51 (11)

51 (11)

50 (12)

48 (16)

Self-care

59

50 (15)

44 (25)

45 (24)

45 (24)

Emotional well-being

47

43 (9)

37 (21)

34 (28)

33 (30)