Garshick et al. compared with the lowest quartile, but dif- on lag), but lung cancer mortality risk statisti- caused by left truncation in a cohort composed ferences were not statistically significant [haz- cally significantly decreased with duration. of prevalent hires combined with a healthy ard ratio (HR) = 1.17–1.19 for 5-year lagged For example, in the 5-year lag cumulative EC worker survivor effect. Left truncation occurs exposures, excluding mechanics]. Associations model excluding mechanics, the HR per year when subjects who were hired before the start with cumulative EC exposure were stronger of work was 0.97 (95% CI = 0.96, 0.99). The of follow-up are included. Inclusion of such for all three lags after adjusting for duration attenuation of relative risk estimates if employ- prevalent hires and variability in susceptibility of employment but did not display a mono- ment duration was not included is consistent to exposure has been shown to cause down- tonic dose response when estimated for the with negative confounding. ward bias between disease and exposure dura- cohort as a whole. However, HRs for 5- and tion (Applebaum et al. 2011). Effects of left Discussion 10-year lagged exposures increased with each truncation were observed in a study of lung quartile when mechanics were excluded, which We performed a retrospective assessment of cancer and silica exposure where exposure was resulted in estimated HR of 1.48 [95% confi- EC exposure and lung cancer mortality in a inversely associated with lung cancer mortality dence interval (CI): 1.05, 2.10] and 1.41 (95% large U.S. trucking industry cohort and found among prevalent hires, despite greater cumula- CI: 0.95, 2.11) for the highest versus lowest that estimated cumulative exposure to EC was tive exposure (Applebaum et al. 2007). We quartiles of 5- and 10-year lagged exposures, positively associated with lung cancer mortal- also observed an inverse association between respectively. Associations were weaker for ity after adjusting for employment duration in employment duration and lung cancer mortal- average EC exposure (5-year lag shown as an addition to race, census region, and calendar ity in a cohort of prevalent hires in the U.S. example) in models adjusting for duration of year. Other than the mechanics, workers with railroad industry (Garshick et al. 2004). employment (Table 4). occupational EC exposure were in driver- or The healthy worker survivor effect is com- Excluding the mechanics, regression models loading dock–related jobs that involved regu- monly presumed to be small or absent for lung incorporating penalized splines for cumulative lar and often continuous exposure to vehicle cancer. However, results from occupational EC indicated that lung cancer risk increased exhaust from diesel and nondiesel sources. lung cancer studies of arsenic, radiation, and with increasing cumulative EC and did not Estimated relative risks were stronger when other diesel-exposed workers suggest otherwise statistically significantly depart from linearity. 1,811 mechanics were excluded. There was a (Arrighi and Hertz-Picciotto 1996; Brown et al. For each 1,000 gμ/m 3-months of cumulative suggestion of a linear exposure–response rela- 2004; Cardis et al. 2007; Neumeyer-Gromen EC, the estimated HR is 1.04 (95% CI: 0.97, tionship, and the strongest associations were et al. 2009). In nuclear industry workers, there 1.11), 1.07 (95% CI: 0.99, 1.15), and 1.09 observed with a 5- and 10-year cumulative was no association between lung cancer mortal- (95% CI: 0.99, 1.20) for no exposure lag, a exposure lag with a HR of 1.07 (95% CI: ity and cumulative radiation exposure (lag 10) 5-year exposure lag, and a 10-year exposure lag, 0.99, 1.15) and 1.09 (95% CI: 0.99, 1.20), without adjustment for duration (Cardis et al. respectively (Table 5). There was no associa- respectively. Average exposure was not associ- 2007). In diesel-exposed potash miners, adjust- tion with average EC as a continuous covariate ated with lung cancer mortality. ing for time since hire resulted in a stronger (p = 0.71 for the no lag and p = 0.69 for the Estimated relative risks decreased with association between lung cancer mortality and 5-year lag model) (data not shown). employment duration, which suggests that exposure (Neumeyer-Gromen et al. 2009). In Duration of employment was correlated duration was a surrogate for time-varying a study of autoworkers, Chevrier et al. (2012) with cumulative EC (r = 0.55–0.74, depending health status. This finding was likely due to bias assessed different analytical methods and also Table 4. Lung cancer HRs associated with each quartile of cumulative and average EC, with and without adjustment for duration of work. Entire cohort (n = 31,135) Cohort excluding mechanics (n = 29,324) HR (95% CI) HR (95% CI) HR (95% CI) HR (95% CI) Person- Lung cancer unadjusted for adjusted for Person- Lung cancer unadjusted for adjusted for Exposure years deaths duration of work duration of work years deaths duration of work duration of work Cumulative EC (µg/m3-months) No lag < 530 106,272 153 Reference Reference 105,868 153 Reference Reference 530 to < 1,061 106,208 194 1.13 (0.90, 1.42) 1.24 (0.98, 1.57) 105,312 193 1.13 (0.90, 1.42) 1.25 (0.99, 1.60) 1,061 to < 2,076 106,149 209 1.14 (0.89, 1.47) 1.30 (0.99, 1.70) 102,534 202 1.13 (0.87, 1.46) 1.30 (0.99, 1.72) ≥ 2076 106,039 223 0.98 (0.74, 1.29) 1.16 (0.86, 1.57) 86,600 193 1.02 (0.76, 1.36) 1.24 (0.89, 1.71) p for trend 0.37 0.92 0.63 0.71 5-year lag < 371 106,359 122 Reference Reference 105,513 122 Reference Reference 371 to < 860 106,223 193 1.18 (0.92, 1.51) 1.30 (1.01, 1.68) 104,909 191 1.18 (0.92, 1.52) 1.31 (1.01, 1.71) 860 to < 1,803 106,114 208 1.16 (0.88, 1.53) 1.35 (1.01, 1.81) 102,496 202 1.17 (0.88, 1.55) 1.38 (1.02, 1.87) ≥ 1,803 105,972 256 1.12 (0.83, 1.52) 1.36 (0.98, 1.89) 87,397 226 1.19 (0.86, 1.63) 1.48 (1.05, 2.10) p for trend 0.97 0.39 0.61 0.16 10-year lag < 167 106,409 114 Reference Reference 104,329 112 Reference Reference 167 to < 596 106,213 183 1.04 (0.79, 1.37) 1.14 (0.86, 1.52) 104,487 179 1.06 (0.80, 1.40) 1.17 (0.88, 1.57) 596 to < 1,436 106,120 205 1.01 (0.74, 1.37) 1.18 (0.85, 1.64) 102,712 202 1.05 (0.77, 1.45) 1.26 (0.90, 1.78) ≥ 1,436 105,926 277 1.03 (0.72, 1.45) 1.25 (0.86, 1.82) 88,786 248 1.12 (0.78, 1.61) 1.41 (0.95, 2.11) p for trend 0.96 0.39 0.57 0.15 Average exposure, 5-year lag (µg/m3) < 3.6 106,304 146 Reference Reference 105,930 146 Reference Reference 3.6 to < 5.4 106,153 211 1.15 (0.93, 1.43) 1.15 (0.93, 1.43) 105,950 211 1.15 (0.93, 1.43) 1.15 (0.93, 1.43) 5.4 to < 7.9 106,093 221 1.11 (0.89, 1.39) 1.12 (0.90, 1.40) 105,512 221 1.11 (0.89, 1.39) 1.12 (0.89, 1.40) ≥ 7.9 106,117 201 1.06 (0.84, 1.34) 1.08 (0.85, 1.36) 82,922 163 1.11 (0.87, 1.43) 1.13 (0.88, 1.44) p for trend 0.97 0.88 0.61 0.53 All models adjusted for race, calendar year of follow-up, and census region. 1304 120 | number 9 | September 2012 • Environmental Health Perspectives ovlume