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Table 3 Register data

From: Assessment of selection bias in a health survey of children and families – the IDEFICS Sweden-study

   IDEFICS population Reference population p-value
n=1 431 n= 1 825
Maternal characteristics     
  BMI 23.8 (3.7) 24.0 (3.9) 0.479
n = 1 158 n = 1 305
  Age (years) 37.8 (4.5) 37.0 (5.2) <0.001
n = 1 370 n = 1 557
Smoking 3 months before pregnancy Not smoking 1 071 (86.9%) 1 095 (80.1%)  
  1–9 cigarettes/day 73 (5.9%) 133 (9.7%)  
  10 or more cigarettes/day 88 (7.1%) 139 (10.2%) <0.001
Family characteristics     
Educational level ISCED (1–2) Low 18 (1.3%) 49 (2.7%)  
  ISCED (3–4) Medium 492 (34.4%) 820 (45.0%)  
  ISCED (5–6) High 921 (64.4%) 953 (52.3%) <0.001
Family type Single parent 112 (7.8%) 269 (14.7%)  
  Married or co-habiting 1 319 (92.2%) 1 556 (85.3%) <0.001
Number of children One child 168 (11.7%) 287 (15.7%)  
  Two or more children 1 263 (88.3%) 1 538 (84.3%) <0.01
Single or twin birth Single birth 1 327 (96.9%) 1 510 (97%)  
  Twin birth 43 (3.1%) 47 (3.0%) 0.934
Parental origin Swedish 1 337 (93.4%) 1 599 (87.6%)  
  Foreign 94 (6.6%) 226 (12.4%) <0.001
Family economy Disposable income/familya 4 943 (2 039) 4 651 (2 527) <0.001
n = 1 431 n = 1 825
  Parental personal incomea (one parent) 2 827 (2 445) 2 078 (1 814) 0.004
n = 112 n = 269
  Social welfare pension/family 26 (1.8%) 85 (4.7%) <0.001
  Disability pension/family 45 (3.1%) 103 (5.6%) <0.001
  Unemployment compensation/family 141 (9.9%) 243 (13.3%) 0.003
  Financial study assistance/family 106 (7.4%) 194 (10.6%) 0.002
  1. Maternal characteristics at enrollment in maternity care, and family socioeconomic and sociodemographic characteristics in the IDEFICS and reference populations. Data are presented as the mean with standard deviation (SD) or number and percentage (%).
  2. a The income is in hundred Swedish krona (SEK), e.g. 4 943= SEK 494 300 per year; this sum was equivalent to €53 449 in 2007 (€ 1 = SEK 9.2481).