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Table 1 The relationship between the proportion of measures and subjects versus intra-class correlation relative to the proportion needed when only one measure is employed (top rows). The lower table shows the effective percentage increase in study efficiency (in terms of subjects) that can be achieved by taking multiple samples. For example, a two-sample study with an ICC of 0.5 is equivalent to a one-sample study with 33% more subjects (as is also apparent from the first table in the 75 to 100 difference)

From: Employing multiple synchronous outcome samples per subject to improve study efficiency

%Measures/% Subjects
Intra-Class Correlation
Measures 0 0.15 0.35 0.5 0.65 0.85 0.9 1
1 100 / 100 100 / 100 100 / 100 100 / 100 100 / 100 100 / 100 100 / 100 100 / 100
2 100 / 50 116 / 58 136 / 68 150 / 75 166 / 83 186 / 93 190 / 95 200 / 100
3 99 / 33 129 / 43 171 / 57 201 / 67 231 / 77 270 / 90 279 / 93 300 / 100
4 100 / 25 144 / 36 204 / 51 252 / 63 296 / 74 356 / 89 372 / 93 400 / 100
5 100 / 20 160 / 32 240 / 48 300 / 60 360 / 72 440 / 88 460 / 92 500 / 100
Effective Sample Size
Measures         
1 100 100 100 100 100 100 100 100
2 200 174 148 133 121 108 105 100
3 300 231 176 150 130 111 107 100
4 400 276 195 160 136 113 108 100
5 500 313 208 167 139 114 109 100