Characteristics of NorTwinCan twin cohorts included in the analyses by zygosity and sex (individuals with smoking data)
| Sex and zygosity of twin individuals | Denmark | Finland | Norway | Sweden | Total |
|---|---|---|---|---|---|
| Males | |||||
| MZ | 5309 | 3421 | 2532 | 8525 | 19 787 |
| DZ | 8263 | 8035 | 3313 | 14 262 | 33 873 |
| UZ | 480 | 1247 | – | 1131 | 2858 |
| All males | 14 052 | 12 703 | 5845 | 23 918 | 56 519 |
| Females | |||||
| MZ | 6570 | 3940 | 3074 | 10 141 | 23 725 |
| DZ | 9525 | 8092 | 3788 | 16 617 | 38 022 |
| UZ | 473 | 1049 | – | 996 | 2518 |
| All females | 16 568 | 13 081 | 6862 | 27 754 | 64 265 |
| Birth cohort included | 1870–1982 | 1880–1957 | 1915–1960 | 1886–1958 | |
| 1st Year of assessment of smoking and start of lung cancer occurrence follow-up | 1959 | 1975 | 1980 | 1961 | |
| End of follow-up for lung cancer occurrence | 2010 | 2011 | 2009 | 2010 | |
| Number of incident lung cancers | 354 | 341 | 152 | 661 | 1508 |
| Mean age at baseline (years) | 49.0 | 36.2 | 38.3 | 38.9 | |
| Mean follow-up time (years) | 10.2* | 30.1 | 24.6 | 32.1 | |
The 5376 twins with unknown zygosity are included in the table but are excluded from pairwise analysis.
*In Denmark, smoking data came from eight surveys conducted from 1959 to 2002.
DZ, dizygotic; MZ, monozygotic.