Table 4
Estimates of bias in cumulative exposure-disease trends derived via Poisson regression under four rules for exposure categorisation and three methods for exposure score assignment; simulation analyses under the assumption that exposure intensity conforms to an exponential distribution
| Exposure categorisation | Score assignment | ||
|---|---|---|---|
| Category midpoint | Category mean | Cell specific mean | |
| Bias, λ | Bias, λ | Bias, λ | |
Coefficient of bias,  . Estimates were derived after 100 repetitions of each simulation. | |||
| 5 categories | 0.50 | 1.24 | 1.21 |
| Based on quintiles of the cumulative exposure distribution | |||
| 10 categories | 0.58 | 1.11 | 1.13 |
| Based on deciles of the cumulative exposure distribution | |||
| 5 categories | 0.73 | 1.15 | 1.14 |
| Based on quintiles of the cumulative exposure distribution among cases | |||
| 10 categories | 0.84 | 1.08 | 1.08 |
| Based on deciles of the cumulative exposure distribution among cases | |||