Table 3.
Hazard ratios (HR) and 95% confidence intervals (95% CI) of aggressive prostate cancer in the Norwegian Offshore Petroleum Workers cohort
| Complete study sample (n = 2159)a |
Multiple imputation (n = 2355)a |
|||
|---|---|---|---|---|
| No. of cases | Person-years | HR (95% CI)f | HR (95% CI)f | |
| 10-year lag | ||||
| Rollover shift work duration (years)b,c,d,e | ||||
| 0 | 112 | 16 957.55 | 1.00 (reference) | 1.00 (reference) |
| >0–<3 | 38 | 5304.36 | 1.23 (0.84–1.78) | 1.26 (0.88–1.81) |
| 3–<9 | 41 | 5571.12 | 1.20 (0.83–1.72) | 1.23 (0.87–1.74) |
| 9–<16 | 40 | 5550.14 | 1.14 (0.78–1.68) | 1.15 (0.80–1.65) |
| 16–<19.5 | 18 | 1765.68 | 1.17 (0.69–1.95) | 1.22 (0.74–2.02) |
| 19.5–33.3 | 26 | 1477.74 | 1.97 (1.23–3.14) | 1.92 (1.21–3.05) |
| P–trendg | 0.047 | 0.046 | ||
| 15–year lag | ||||
| Rollover shift work duration (years)b,c,d,e | ||||
| 0 | 113 | 18 138.75 | 1.00 (reference) | 1.00 (reference) |
| >0–<3 | 37 | 5477.71 | 1.16 (0.80–1.70) | 1.20 (0.83–1.73) |
| 3–<9 | 45 | 6182.65 | 1.24 (0.87–1.76) | 1.25 (0.89–1.75) |
| 9–<16 | 38 | 4810.03 | 1.05 (0.72–1.55) | 1.06 (0.73–1.54) |
| 16–<19.5 | 22 | 1149.64 | 1.72 (1.06–2.78) | 1.79 (1.12–2.86) |
| 19.5–33.3 | 20 | 867.82 | 1.97 (1.16–3.34) | 1.92 (1.15–3.21) |
| P–trendg | 0.018 | 0.015 | ||
| 20–year lag | ||||
| Rollover shift work duration (years)b,c,d,e | ||||
| 0 | 117 | 20 410.65 | 1.00 (reference) | 1.00 (reference) |
| >0–<3 | 41 | 5950.03 | 1.21 (0.84–1.74) | 1.18 (0.83–1.69) |
| 3–<9 | 48 | 5958.95 | 1.20 (0.85–1.69) | 1.19 (0.86–1.66) |
| 9–<16 | 46 | 3397.82 | 1.34 (0.94–1.93) | 1.38 (0.97–1.95) |
| 16–<19.5 | 15 | 578.60 | 1.98 (1.12–3.51) | 1.92 (1.09–3.37) |
| 19.5–33.3 | 9 | 343.46 | 1.99 (0.95–4.16) | 1.90 (0.92–3.95) |
| P-trendg | 0.009 | 0.007 | ||
Any workers without pure day work (for complete and multiple imputed data) were excluded to ensure the reference category (0 years) contained workers with day work only, n varied with lag period as shift type exposure changed among workers.
Adjusted for year of first employment and education, and stratified by 10-year birth cohorts.
Complete work history i.e. up to eight employments as an offshore worker.
Missing: rollover shift work duration (n = 119), year of first employment (n = 1), education (n = 21).
Categorized into non-exposed (0) and quartiles among exposed. To capture the tail of the distribution, the upper quartile was divided into two by its median.
Cox regression adapted to a case cohort design with age as the time scale.
Modelled as a continuous variable to test for linear trend.