Table 3

 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 a lognormal (0,1) distribution

Exposure categorisationScore assignment
Category midpointCategory meanCell specific mean
Bias, λBias, λBias, λ
Coefficient of bias, Embedded Image. Estimates were derived after 100 repetitions of each simulation.
5 categories0.421.161.24
Based on quintiles of the cumulative exposure distribution
10 categories0.501.041.12
Based on deciles of the cumulative exposure distribution
5 categories0.670.981.04
Based on quintiles of the cumulative exposure distribution among cases
10 categories0.780.991.02
Based on deciles of the cumulative exposure distribution among cases