Baseline characteristics of respondents and non-respondents to the 2018 follow-up questionnaire (N=5817)
| Characteristic | Responders* | Non-responders† | ||
| No asthma diagnosis N=2313 | Asthma N=265 | No asthma diagnosis N=2896 | Asthma N=343 | |
| Age | ||||
| Mean (SD) | 55.6 (11.2) | 54.2 (12.0) | 53.2 (13.0) | 50.9 (13.9) |
| Unpaired t-test (p value)‡ | 0.058 | 0.006 | ||
| Missing=58 | ||||
| Gender | ||||
| Male (n, %) | 2238 (97.4%) | 255 (97.3%) | 2805 (98.2%) | 331 (96.8%) |
| χ2 test (p value)§ | 0.840 | 0.091 | ||
| Missing=59 | ||||
| Smoking status (n, %) | ||||
| Current | 151 (7.1%) | 13 (5.3%) | 291 (11.1%) | 25 (8.0%) |
| Ex-smoker | 555 (26.0%) | 83 (33.6%) | 730 (27.9%) | 88 (28.3%) |
| Never-smoker | 1425 (66.9%) | 151 (61.1%) | 1592 (60.9%) | 198 (63.7%) |
| χ2 test (p value)§ | 0.036 | 0.242 | ||
| Missing=515 | ||||
| Pack-years¶ | ||||
| Mean (SD) | 16.1 (17.9) | 15.8 (22.4) | 16.2 (18.4) | 14.2 (15.8) |
| Unpaired t-test (p value)‡ | 0.909 | 0.325 | ||
| Median (IQR) | 10.3 (3.5–22) | 8.3 (3–20) | 10 (3.5–22.5) | 10.3 (3.6–20) |
| Missing=563 | ||||
| Family history of asthma (n, %) | ||||
| Yes | 287 (12.4%) | 101 (38.1%) | 394 (13.6%) | 132 (38.5%) |
| No | 2026 (87.6%) | 164 (61.9%) | 2502 (86.4%) | 211 (61.5%) |
| χ2 test (p value)§ | <0.001 | <0.001 | ||
| Missing=0 | ||||
| Years worked or lived on a farm | ||||
| Mean (SD) | 36.5 (22.5) | 31.7 (22.8) | 37.5 (21.5) | 35.0 (21.5) |
| Unpaired t-test (p value)‡ | 0.002 | 0.052 | ||
| Median (IQR) | 40 (18–55.0) | 38.5 (7.5–51.3) | 40 (22–54.4) | 38.1 (20.5–52.2) |
| Missing=183 | ||||
| Years spent working with pesticides | ||||
| Mean (SD) | 25.0 (11.5) | 24.2 (11.3) | 23.0 (12.2) | 21.1 (12.3) |
| Unpaired t-test (p value)‡ | 0.255 | 0.011 | ||
| Missing=78 | ||||
*Number of individuals who responded to the baseline and the follow-up questionnaire, and their doctor diagnosed asthma status at baseline
†Number of individuals who did not respond to the follow-up questionnaire, and their doctor diagnosed asthma status at baseline
‡P value for a bootstrapped unpaired t-test comparing those with and those without an asthma diagnosis
§P value for Fisher’s exact χ2 test comparing those with and those without an asthma diagnosis
¶Pack-years = (number of cigarettes smoked a day/20) multiplied by the number of years smoked; for those who smoke(d)
N or n, count.