Table 1

Characteristics of study participants (n=2671)

CharacteristicN%Mean age/SD at school entry
Gender
 Girls132949.86.63/0.31
 Boys134250.26.68/0.30
Age at school entry (years)
 Less than 6.00150.65.97/0.02
 6.00 to 6.2427710.46.16/0.06
 6.25 to 6.4960122.56.38/0.07
 6.50 to 6.7467325.26.62/0.07
 6.75 to 6.9968225.56.88/0.07
 7.00 or older42315.87.09/0.06
Family structure
 Nuclear family202275.76.65/0.31
 Single-parent family, foster parents, other63223.76.66/0.30
 Missing170.66.57/0.22
CASMIN classification
 Still in education/0.5521.96.62/0.27
 1a/1.000~
 1b/1.740.16.64/0.33
 2b/2.880.36.57/0.30
 1 c/3.0572.16.66/0.30
 2a/3.636113.56.68/0.31
 2c-gen/3.7341.36.66/0.31
 2c-voc/4.848418.16.67/0.31
 3a/6.141915.76.67/0.30
 3b/7.0124646.66.64/0.30
 Missing60.26.74/0.18
Migrant background
 No218581.86.66/0.31
 Yes48118.06.65/0.31
 Missing50.26.72/0.19
Gestational age at birth
 Term129948.66.66/0.30
 Preterm923.46.71/0.27
 Missing*139348.06.65/0.31
Hyperactivity-Inattention Subscale score at baseline
 035813.46.66/0.29
 126910.16.66/0.31
 22358.86.67/0.30
 31786.76.68/0.30
 41314.96.69/0.30
 5762.86.60/0.27
 6230.96.70/0.28
 790.36.71/0.22
 890.36.58/0.42
 900.0~
 1000.0~
 Missing*138351.86.65/0.31
  • *Due to the open cohort study design, the parental questionnaire at baseline was available for 1288 children only.