Definitions of explanatory variables.

aTime-dependent indicates that these variables were available at 4, 6, 7, 8, and 10 years of age and thus were treated as time-dependent explanatory variables in the analysis. If a variable was only measured once and occurred at or before baseline (4 y) it was treated as a ‘risk factor’ (time-stable).bMissing at 4 y of age for all children, value at age 3.5 y was carried forward to age 4.cFor more information on how this variable was calculated and interpreted, please see reference 32.dMeasured every other data collection cycle for all children (value at age 6 was carried forward for age 7).