Table 1

Characteristics of NorTwinCan twin cohorts included in the analyses by zygosity and sex (individuals with smoking data)

Sex and zygosity of twin individualsDenmarkFinlandNorwaySwedenTotal
 MZ530934212532852519 787
 DZ82638035331314 26233 873
 All males14 05212 703584523 91856 519
 MZ65703940307410 14123 725
 DZ95258092378816 61738 022
 All females16 56813 081686227 75464 265
Birth cohort included1870–19821880–19571915–19601886–1958
1st Year of assessment of smoking and start of lung cancer occurrence follow-up1959197519801961
End of follow-up for lung cancer occurrence2010201120092010
Number of incident lung cancers3543411526611508
Mean age at baseline (years)
Mean follow-up time (years)10.2*30.124.632.1
  • 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.