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Table 7 Percentage of trials re-estimating the sample size, conditional power among trials that re-estimated the sample size and overall mean and median sample size for sample size re-estimation using conditional power

From: Impact of misspecifying the distribution of a prognostic factor on power and sample size for testing treatment interactions in clinical trials

θ Planned distribution of the prognostic factor Planned n t Percent re-estimating sample size Empirical conditional power Mean sample size Median sample size
Misspecification of the prognostic factor: 0%
5 10% 1,418 37.44% 0.9471 2,500 1,418
20% 798 37.30% 0.9566 1,470 798
30% 608 37.74% 0.9671 1,143 608
40% 532 38.00% 0.9689 984 532
50% 512 39.44% 0.9660 989 512
15 10% 178 37.44% 0.9701 327 178
20% 100 40.48% 0.9674 202 100
30% 78 39.28% 0.9695 150 78
40% 68 42.02% 0.9719 155 68
50% 64 43.58% 0.9748 154 64
Misspecification of the prognostic factor: -5%
5 10% 1,418 49.70% 0.8881 3,568 1,418
20% 798 43.12% 0.9429 1,696 798
30% 608 40.98% 0.9458 1,231 608
40% 532 38.56% 0.9570 1,062 532
50% 512 38.82% 0.9629 987 512
15 10% 178 45.00% 0.8738 402 178
20% 100 42.54% 0.9342 219 100
30% 78 43.56% 0.9660 171 78
40% 68 43.38% 0.9779 153 68
50% 64 44.40% 0.9770 155 64
Misspecification of the prognostic factor: -15%
5 10% 1,418 -- -- -- --
20% 798 51.98% 0.7618 2,425 865
30% 608 47.34% 0.8952 1,439 608
40% 532 44.96% 0.9346 1,155 532
50% 512 41.42% 0.9546 1,028 512
15 10% 178 -- -- -- --
20% 100 48.70% 0.7573 267 100
30% 78 46.80% 0.9167 190 78
40% 68 47.38% 0.9565 161 68
50% 64 44.50% 0.9685 148 64
Misspecification of the prognostic factor: +5%
5 10% 1,418 25.94% 0.9861 1,984 1,418
20% 798 33.26% 0.9747 1,310 798
30% 608 35.76% 0.9676 1,096 608
40% 532 37.68% 0.9618 975 532
50% 512 39.24% 0.9623 969 512
15 10% 178 28.32% 0.9845 263 178
20% 100 35.36% 0.9762 177 100
30% 78 37.42% 0.9840 153 78
40% 68 43.32% 0.9797 150 68
50% 64 45.72% 0.9790 157 64
Misspecification of the prognostic factor: +15%
5 10% 1,418 15.04% 0.9960 1,472 1,418
20% 798 27.34% 0.9824 1,159 798
30% 608 34.22% 0.9673 1,007 608
40% 532 38.58% 0.9725 1,026 532
50% 512 41.56% 0.9644 1,045 512
15 10% 178 14.40% 0.9944 190 89
20% 100 30.38% 0.9888 159 100
30% 78 37.62% 0.9856 149 78
40% 68 43.78% 0.9753 151 68
50% 64 48.00% 0.9708 168 64