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Design of the flexible two-phase study for Example 1 |
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| Disease Status (D) |
Metal-workers Z (τij) |
Fixed number of subjects to be included in Phase Two (nij) |
Expected Phase One numbers of subjects to be screened (Nij) |
Expected Proportion of MWF exposure within strata § X(πijk) |
Expected distribution of subjects by MWF in Phase Two |
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| N0 = Max(160/20%, 40/80%) = 800 |
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| Control |
No (80%*) |
40 |
800*80% = 640 |
No (97.5%*) |
40*97.5% = 39 |
| Yes (2.5%*) |
40*2.5% = 1 |
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| Yes (20%*) |
160 |
800*20% = 160 |
No (75%*) |
160*75% = 120 |
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| Yes (25%*) |
160*25% = 40 |
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| N1 = Max(85/23.4%, 20/76.6%) = 364 |
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| Case |
No (76.6%#) |
20 |
364*76.6% = 278.8 |
No (95.1%#) |
20*95.1% = 19.02 |
| Yes (4.9%#) |
20*4.9% = 0.98 |
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| Yes (23.4%#) |
85 |
364*23.4% = 85 |
No (60%#) |
85*60% = 51 |
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| Yes (40%#) |
85*40% = 34 |
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* Values of parameters fixed in Table 1 # Values of parameters computed from parameter values fixed in Table 1 (see Appendix 2) § In Phase One controls, the overall expected percentage of MWF exposure is equal to 7%, that is, 2% = 2.5% of 80% non-metal-workers plus 5% = 25% of 20% metal-workers. Similar computations lead to 13% MWF exposure in cases. | |||||
Wild et al. Epidemiologic Perspectives & Innovations 2008 5:4 doi:10.1186/1742-5573-5-4 |
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