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Table 1 Characteristics of the study population

From: Risk of epilepsy in opposite-sex and same-sex twins: a twin cohort study

  Female twins Male twins
Characteristics OSa (n=11,078) SSa (n=19,186) OSa (n=11,080) SSa (n=20,207)
N (%) N (%) N (%) N (%)
Zygosity
 Monozygotic . 3,425 (17.9) . 3,436 (17.0)
 Dizygotic 11,078 (100) 5,719 (29.8) 11,080 (100) 6,030 (29.8)
 Unknown . 10,042 (52.3) . 10,741 (53.2)
Maternal age at birth (years)  
 <25 976 (8.8) 2,662 (13.9) 985 (8.9) 2,727 (13.5)
 25-29 3,364 (30.4) 6,514 (34.0) 3,353 (30.3) 6,745 (33.4)
 30-35 4,421 (39.9) 6,828 (35.6) 4,421 (39.9) 7,357 (36.4)
 35-39 2,029 (18.3) 2,796 (14.6) 2,033 (18.3) 3,021 (15.0)
 40+ 288 (2.6) 386 (2.0) 288 (2.6) 357 (1.8)
Paternal age at birth (years)
 <30 2,727 (24.6) 5,891 (30.7) 2,728 (24.6) 6,398 (31.7)
 30-39 6,883 (62.1) 11,088 (57.8) 6,880 (62.1) 11,468 (56.8)
 40+ 1,374 (12.4) 2,032 (10.6) 1,375 (12.4) 2,091 (10.3)
 Missing 94 (0.8) 175 (0.9) 97 (0.9) 250 (1.2)
Maternal completed highest education
 Primary and lower secondary 1,902 (17.2) 3,600 (18.8) 1,914 (17.3) 3,763 (18.6)
 Upper and post-secondary 4,477 (40.4) 7,801 (40.7) 4,468 (40.3) 8,210 (40.6)
 Tertiary 4,560 (41.2) 7,476 (39.0) 4,558 (41.1) 7,979 (39.5)
 Missing 139 (1.3) 309 (1.6) 140 (1.3) 255 (1.3)
Paternal completed highest education
 Primary and lower secondary 2,038 (18.4) 3,612 (18.8) 2,029 (18.3) 3,909 (19.3)
 Upper and post-secondary 5,218 (47.1) 9,140 (47.6) 5,231 (47.2) 9,485 (46.9)
 Tertiary 3,561 (32.1) 5,867 (30.6) 3,557 (32.1) 6,190 (30.6)
 Missing 261 (2.4) 567 (3.0) 263 (2.4) 623 (3.1)
Calendar year of birth
 1977-1984 1,234 (11.1) 2,806 (14.6) 1,231 (11.1) 3,249 (16.1)
 1985-1994 2,451 (22.1) 4,994 (26.0) 2,463 (22.2) 4,953 (24.5)
 1995-1999 2,212 (20.0) 3,414 (17.8) 2,213 (20.0) 3,768 (18.6)
 2000-2004 2,553 (23.0) 3,913 (20.4) 2,550 (23.0) 4,114 (20.4)
 2005-2009 2,628 (23.7) 4,059 (21.2) 2,623 (23.7) 4,123 (20.4)
  1. aOS opposite-sex twins, i.e., twins with an opposite sex co-twin, SS same-sex twins, i.e., twins with a same sex co-twin