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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)