Table 1.
Characteristics of the study sample (n = 2355) in the Norwegian Offshore Petroleum Workers Cohort
| Variablesa | Cases (n = 299) | Non-cases (n = 2056) |
|---|---|---|
| Age at start of follow-up (years), median (range) | 52 (32–73) | 54 (20–80) |
| 10-year birth cohort, n (%) | ||
| 1915–24 | 0 (0.0) | 25 (1.2) |
| 1925–34 | (NA) | 325 (15.8) |
| 1935–44 | 99 (33.1) | 748 (36.4) |
| 1945–54 | 143 (47.8) | 676 (32.9) |
| 1955–64 | 37 (12.4) | 236 (11.5) |
| 1965–79 | <5 (NA) | 46 (2.2) |
| Education, n (%) | ||
| Compulsory | 44 (14.7) | 327 (15.9) |
| Vocational | 144 (48.2) | 1046 (50.9) |
| Upper secondary | 51 (17.0) | 278 (13.5) |
| University/college | 57 (19.1) | 387 (18.8) |
| Missing | 3 (1.00) | 18 (0.9) |
| Anthropometric factors | ||
| Height (cm), median (range)b | 180 (160–199) | 179 (156–200) |
| Weight (kg), median (range)b | 82 (54–130) | 82 (48–184) |
| BMI (kg/m2) n (%), median (range)b | 25.8 (18–36) | 25.6 (13.7–60.8) |
| Work history | ||
| Year of first employment (years), median (range) | 1980 (1965, 1997) | 1979 (1965, 1998) |
| Year of first employment, n (%) | ||
| 1965–74 | 36 (12.0) | 293 (14.3) |
| 1975–84 | 185 (61.9) | 1220 (59.3) |
| 1985–94 | 72 (24.1) | 472 (22.9) |
| 1995–98 | 6 (2.0) | 70 (3.4) |
| Missing | 0 (0.0) | 1 (0.1) |
| Main occupational activity in last position, n (%) | ||
| Production and process | 26 (8.7) | 184 (8.9) |
| Drilling and well maintenance | 27 (9.0) | 175 (8.5) |
| Maintenance/inspection/deck construction | 143 (47.8) | 1055 (51.3) |
| Catering/office/administration | 51 (17.1) | 293 (14.3) |
| Miscellaneous | 50 (16.7) | 324 (15.8) |
| Missing | 2 (0.7) | 25 (1.2) |
| Total employment duration (years), median (range) | 12.3 (0.09–30.9) | 12.2 (0.09–33.5) |
| Total employment duration (years) in quartiles, n (%)b | ||
| <6 years | 77 (25.8) | 530 (25.8) |
| 6–<12 years | 70 (23.4) | 488 (23.7) |
| 12–<18 years | 74 (24.7) | 511 (24.9) |
| ≥18 years | 78 (26.1) | 526 (25.6) |
| Work schedule, n (%)b | ||
| Day work only | 112 (37.5) | 857 (41.7) |
| Night work only | <5 (NA) | 32 (1.6) |
| Rollover work only | 112 (37.5) | 745 (36.2) |
| Mixed work | <100 (NA) | 320 (15.6) |
| Missing | 17 (5.6) | 102 (4.9) |
| Duration by work schedulec | ||
| Day work (years), median (range) | 8.0 (0.09–28.5) | 10.0 (0.08–32.5) |
| Night work (years), median (range) | 2.0 (0.2–8.0) | 4.2 (0.08–23.2) |
| Rollover shift (years), median (range) | 10 (0.3–30.9) | 8.8 (0.04–33.5) |
| Rollover shift work duration (years), n (%)d,e | ||
| 0 | 118 (39.5) | 912 (44.4) |
| >0–<3 | 38 (12.7) | 267 (13.0) |
| 3–<9 | 39 (13.0) | 275 (13.4) |
| 9–<16 | 39 (13.0) | 266 (12.9) |
| 16–<19.5 | 20 (6.7) | 118 (5.7) |
| >19.5 | 28 (9.4) | 116 (5.6) |
| Missing work schedule | 17 (5.7) | 102 (5.0) |
| Duration (years) of chlorinated degreaser exposure, n (%) | ||
| 0 | 49 (16.4) | 325 (15.8) |
| <Median | 123 (41.1) | 881 (42.9) |
| ≥Median | 127 (42.5) | 850 (41.3) |
| Cumulative chlorinated degreaser exposure, n (%)f | ||
| 0 | 49 (16.4) | 325 (15.8) |
| <Median | 121 (40.5) | 869 (42.3) |
| ≥Median | 129 (43.1) | 862 (41.9) |
BMI, body mass index; NA, not available.
All numbers up to five are listed as <5 due to European Union (EU) General Data Protection Regulations (GDPR), unless this only concerns missing. If only one cell per variable lists a number <5, the next smallest number is listed as <25, <50 or <100.
Missing: Height (n = 35); weight (n = 38); body mass index (BMI) (n = 41); employment duration (n = 1); work schedule (n = 119).
Workers with completely missing information on day, night and rollover shift work (n = 119) were excluded when calculating the median.
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.
Any workers with rollover shift work were included in the exposure categories.
Cumulative exposure: job-exposure matrix (JEM) rating multiplied by duration (in years) for each employment period and summarized for each individual from the start of employment until 31 December 1998.