2.5. Randomization
EVENT
Randomization was done by a statistician at the University of California Davis by assigning the study ID numbers to the four study arms, using a block randomization scheme with block lengths of four or eight. In the event that multiple siblings in the target age range resided in the same household, only the youngest was enrolled. In the case of twins, both twins were assigned to the same group and received all study-related interventions and follow-up, but only one was randomly selected for inclusion in the data analyses.