Table 2

Exposure-response analyses of butadiene or styrene ppm-years and leukaemia: number (N) of cases, adjusted rate ratio (RR) with 95% CI by exposure quartile, beta-coefficient (β) with 95% CI and trend p value

 1261.040.60 to 1.83271.120.61 to 2.07
 2261.370.76 to 2.46271.120.59 to 2.11
 3251.600.87 to 2.94281.790.93 to 3.45
 4262.531.37 to 4.67271.961.00 to 3.82
 All person-time: β(95% CI), trend p value, AIC, N‡2.55×10−4((0.52 to 4.57)×10−4), p=0.014, AIC=2384, N=1321.04×10−3((−0.26 to 2.33)×10−3), p=0.116, AIC=2386, N=132
 Exposed person-time:
 β(95% CI), trend p value, AIC, N
2.50×10−4((0.27 to 4.73)×10−4), p=0.028, AIC=1786, N=1030.84×10−3((−0.51 to 2.20)×10−3), p=0.220, AIC=1912, N=109
 Exposed person-time ≤95th percentile§: β(95% CI), trend p value, AIC, N9.94×10−4((1.88 to 18.00)×10−4), p=0.016, AIC=1673, N=974.05×10−3((−1.19 to 9.30)×10−3), p=0.130, AIC=1795, N=103
 Styrene <27.00 ppm-years1.34×10−4((−20.94 to 23.61)×10−4), p=0.907, AIC=1340, N=77
 Styrene ≥27.00 ppm-years2.86×10−4((0.38 to 5.34)×10−4), p=0.024, AIC=870, N=55
 Butadiene <121.28 ppm-years−7.26×10−4((−120.19 to 105.67)×10−4), p=0.900, AIC=1415, N=80
 Butadiene ≥121.28 ppm-years4.17×10−4((−12.45 to 20.78)×10−4), p=0.623, AIC=803, N=52
  • *All models used attained age as of each day of follow-up as the time scale. Covariates were age at hire, year of hire, race, sex, plant and ever hourly status, except as follows: for the model ofbutadiene within the stratum ≥27.00 styrene ppm-years, sex was not included due to the lack of events among women; for the model of styrene within the stratum ≥121.28 butadiene ppm-years, sex and ever-hourly were not included due to the lack of events among women and never hourly workers.

  • †Quartile (Q) cutpoints were at the following values of ppm-years: (1) butadiene: Q2, 34.00; Q3, 121.28; Q4, 363.64, maximum=7741.41; (2) styrene: Q2, 5.76; Q3, 27.00; Q4, 60.53, maximum=1203.21.

  • ‡AIC, Akaike information criterion; N, number of cases included in the model.

  • §95th percentile was at 1144 ppm-years for butadiene and 171 ppm-years for styrene.

  • ¶Models used all person-time.