Volume 8, Number 4—April 2002
Research
Sampling Bias in the Molecular Epidemiology of Tuberculosis
Megan B. Murray
Table 2
Monte Carlo means and 95% ranges for the proportion of unique isolates and for odds ratios after sampling a fraction of the complete data set.
| Sampling fraction | 1 | 0.7 | 0.5 | 0.1 |
|---|---|---|---|---|
| Sudan | ||||
| Proportion of reactivated isolates | ||||
| n method | 0.18 | 0.19 (0.18-0.19) | 0.21 (0.19-0.23) | 0.37 (0.30-0.43) |
| “n minus one” method | 0.28 | 0.32 (0.30-0.34) | 0.35 (0.30-0.41) | 0.54 (0.47-0.62) |
| Odds ratiosa | 2 | 1.88 (1.87-1.97) | 1.77 (1.66-1.88) | 1.34 (1.28-1.45) |
| 5 | 4.18 (4.13-4.78) | 3.51 (3.01-4.18) | 1.84 (1.60-2.18) | |
| 10 | 7.52 (7.38-9.27) | 1.84 (1.67-1.84) | 2.37 (2.08-2.99) | |
| New York prisons | ||||
| Proportion of reactivated isolates | ||||
| n method | 0.12 | 0.14 (0.12-0.16) | 0.16 (0.13-0.20) | 0.45 (0.28-0.62) |
| “n minus one” method | 0.33 | 0.36 (0.33-0.38) | 0.39 (0.32-0.45) | 0.67 (0.61-0.73) |
| Odds ratios | 2 | 1.77 (1.60-1.95) | 1.62 (1.45-1.83) | 1.16 (1.12-1.29) |
| 5 | 3.51 (2.73-4.58) | 2.78 (2.18-3.83) | 1.37 (1.25-1.37) | |
| 10 | 5.79 (4.07-8.66) | 4.17 (2.99-6.58) | 1.58 (1.39-2.12) | |
| Algeria | ||||
| Proportion of reactivated isolates | ||||
| n method | 0.43 | 0.48 (0.45-0.51) | 0.16 (0.13-0.20) | 0.45 (0.28-0.62) |
| “n minus one” method | 0.65 | 0.71 (0.69-0.74) | 0.76 (0.69-0.83) | 0.92 (0.81-0.99) |
| Odds ratios | 2 | 1.81 (1.75-1.92) | 1.67(1.45-1.97) | 1.29 (1.18-1.73) |
| 5 | 3.68 (2.79-4.82) | 3.02 (2.99-4.73) | 1.98 (1.77-2.33) | |
| 10 | 6.58 (5.55-8.23) | 5.05 (4.17-6.58) | 2.62 (2.26-3.28) | |
| U.S. prisons | ||||
| Proportion of reactivated isolates | ||||
| n method | 0.29 | 0.33 (0.29-0.39) | 0.37 (0.29-0.48) | 0.68 (0.35-1.00) |
| “n minus one” method | 0.33 | 0.35 (0.31-0.38) | 0.37 (0.32-0.41) | 0.62 (0.50-0.73) |
| Odds ratios | 2 | 1.8 (1.62-1.98) | 1.67 (1.45-1.97) | 1.29 (1.18-1.73) |
| 5 | 3.68 (2.79-4.82) | 3.02 (2.99-4.73) | 2.11 (1.62-5.31) | |
| 10 | 6.86 (5.30-9.66)) | 4.67 (3.02-9.13) | 2.11 (1.62-5.31) | |
| Netherlands | ||||
| Proportion of reactivated isolates | ||||
| n method | 0.49 | 0.62 (0.55-0.69) | 0.62 (0.55-0.69) | 0.89 (0.77-1.00) |
| “n minus one” method | 0.65 | 0.78 (0.72-0.85) | 0.78 (0.72-0.85) | 0.93 (0.79-1.00) |
| Odds ratios | 2 | 1.8 (1.62-1.98) | 1.67 (1.57-1.81) | 1.40 (1.31-1.49) |
| 5 | 3.68 (2.79-4.82) | 3.05 (2.63-3.78) | 2.02 (1.79-2.32) | |
| 10 | 6.86 (5.30-9.66)) | 4.76 (3.86-6.47) | 3.86 (2.39-3.25) | |
aConfidence intervals for odds ratios are based on the results of 2 by 2 tables, with data adjusted for the mean misclassification introduced by sampling.
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