Additional shift work categorisations
| Variable | Cases (n=1142) | Controls (n=1178) | OR | 95% CI |
|---|---|---|---|---|
| Mean (SD%) | Mean (SD%) | |||
| 20% Evening or night shifts* | ||||
| None | 610 (53.8) | 618 (52.4) | – | |
| <15 | 338 (29.8) | 352 (29.9) | 1.00 | 0.83 to 1.21 |
| 15–30 | 129 (11.4) | 160 (13.6) | 0.83 | 0.64 to 1.07 |
| ≥30 | 57 (5.0) | 49 (4.2) | 1.18 | 0.79–1.76 |
| 40% Evening or night shifts* | ||||
| None | 720 (63.5) | 752 (63.8) | – | |
| <15 | 298 (26.3) | 316 (26.8) | 1.01 | 0.83 to 1.22 |
| 15–30 | 86 (7.6) | 95 (8.1) | 0.96 | 0.70 to 1.31 |
| ≥30 | 30 (2.7) | 16 (1.4) | 1.97 | 1.06 to 3.65 |
| 60% Evening or night shifts* | ||||
| None | 876 (77.3) | 903 (76.6) | – | |
| <15 | 200 (17.6) | 228 (19.3) | 0.93 | 0.75 to 1.15 |
| 15–30 | 40 (3.5) | 42 (3.6) | 0.98 | 0.63 to 1.53 |
| ≥30 | 18 (1.6) | 6 (0.5) | 3.09 | 1.22 to 7.84 |
| 80% Evening or night shifts* | ||||
| None | 941 (83.0) | 974 (82.6) | – | |
| <15 | 162 (14.3) | 181 (15.4) | 0.95 | 0.75 to 1.20 |
| 15–30 | 20 (1.8) | 21 (1.8) | 0.98 | 0.53 to 1.82 |
| ≥30 | 11 (1.0) | 3 (0.3) | 3.73 | 1.04 to 13.42 |
| 100% Evening or night shifts* | ||||
| None | 976 (86.1) | 1029 (87.3) | – | |
| <15 | 136 (12.0) | 139 (11.8) | 1.05 | 0.82 to 1.35 |
| 15–30 | 17 (1.5) | 9 (0.8) | 1.93 | 0.86 to 4.36 |
| >30 | 5 (0.4) | 2 (0.2) | 2.63 | 0.51 to 13.64 |
| 5 Year shift work segments (using 50% of time definition)* | ||||
| None | 751 (66.2) | 773 (65.6) | – | |
| 0–4 | 160 (14.1) | 142 (12.1) | 1.18 | 0.92 to 1.52 |
| 5–9 | 85 (7.5) | 119 (10.1) | 0.75 | 0.56 to 1.01 |
| 10–14 | 38 (3.4) | 51 (4.3) | 0.79 | 0.51 to 1.22 |
| 15–19 | 30 (2.7) | 34 (2.9) | 0.93 | 0.56 to 1.54 |
| 20–24 | 26 (2.3) | 27 (2.3) | 1.01 | 0.59 to 1.75 |
| 25–29 | 16 (1.4) | 20 (1.7) | 0.82 | 0.42 to 1.59 |
| 30–34 | 14 (1.2) | 7 (0.6) | 2.05 | 0.82 to 5.11 |
| ≥35 | 14 (1.2) | 6 (0.5) | 2.40 | 0.92 to 6.30 |
| Number of years in jobs with shifts starting or ending between 11 PM and 7 AM† | (N=1063) | (N=1105) | ||
| None | 826 ((77.7) | 906 (82.0) | ||
| <15 | 172 (15.2) | 146 (12.4) | 1.29 | 1.01 to 1.65 |
| 15–30 | 49 (4.3) | 43 (3.7) | 1.27 | 0.83 to 1.95 |
| ≥30 | 16 (1.4) | 10 (0.9) | 1.68 | 0.74 to 3.79 |
*Adjusted for age and centre.
†Adjusted for age, centre, household income, education and age at first mammogram.