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Table 3 Empirical power and percentage of trials switching to the quota sampling scheme for the modified quota sampling method

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 Empirical power Percent of trials switching to quota sampling
Misspecification of the prognostic factor: -5%
5 10% 1,418 0.8012 99.98%
20% 798 0.7736 74.08%
30% 608 0.7802 47.52%
40% 532 0.7932 36.64%
50% 512 0.8060 35.50%
15 10% 178 0.6636 33.04%
20% 100 0.7400 11.06%
30% 78 0.7940 11.84%
40% 68 0.8164 11.90%
50% 64 0.8122 8.48%
Misspecification of the prognostic factor: -15%
5 10% 1,418 -- --
20% 798 0.8022 100.00%
30% 608 0.8024 100.00%
40% 532 0.8058 99.94%
50% 512 0.8090 99.82%
15 10% 178 -- --
20% 100 0.7788 89.06%
30% 78 0.7834 63.64%
40% 68 0.7904 49.70%
50% 64 0.8038 40.00%
Misspecification of the prognostic factor: +5%
5 10% 1,418 0.8000 98.28%
20% 798 0.8090 67.72%
30% 608 0.8278 49.32%
40% 532 0.8092 37.08%
50% 512 0.7984 36.30%
15 10% 178 0.8880 35.14%
20% 100 0.8656 16.62%
30% 78 0.8542 10.94%
40% 68 0.8350 7.86%
50% 64 0.8198 8.60%
Misspecification of the prognostic factor: +15%
5 10% 1,418 0.8738 100.00%
20% 798 0.8010 100.00%
30% 608 0.8092 99.98%
40% 532 0.8088 99.80%
50% 512 0.8064 99.86%
15 10% 178 0.8942 97.82%
20% 100 0.8504 72.44%
30% 78 0.8572 50.72%
40% 68 0.8466 38.48%
50% 64 0.8174 40.88%
  1. The margin of error based on the 99% confidence interval is 0.015.