Model* | Butadiene | Styrene | ||||

N | RR | 95% CI | N | RR | 95% CI | |

Quartile† | ||||||

Unexposed | 29 | 1.0 | ref | 23 | 1.0 | ref |

1 | 26 | 1.04 | 0.60 to 1.83 | 27 | 1.12 | 0.61 to 2.07 |

2 | 26 | 1.37 | 0.76 to 2.46 | 27 | 1.12 | 0.59 to 2.11 |

3 | 25 | 1.60 | 0.87 to 2.94 | 28 | 1.79 | 0.93 to 3.45 |

4 | 26 | 2.53 | 1.37 to 4.67 | 27 | 1.96 | 1.00 to 3.82 |

Trend | ||||||

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=132 | 1.04×10^{−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=103 | 0.84×10^{−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, N | 9.94×10^{−4}((1.88 to 18.00)×10^{−4}), p=0.016, AIC=1673, N=97 | 4.05×10^{−3}((−1.19 to 9.30)×10^{−3}), p=0.130, AIC=1795, N=103 | ||||

Stratified¶ | ||||||

Styrene <27.00 ppm-years | 1.34×10^{−4}((−20.94 to 23.61)×10^{−4}), p=0.907, AIC=1340, N=77 | |||||

Styrene ≥27.00 ppm-years | 2.86×10^{−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-years | 4.17×10^{−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.