|Characteristic||Children With ASD (N = 256), %||Controls (N = 752), %||Pa|
|Child's year of birth|
|Child's age at time of interview/assessment, y|
|Birth weight, g|
|Biological mother's age at birth of child, y|
|Biological father's age at birth of child, y|
|Mother's education level|
|High school graduate||15||15|
Percentages of cases and controls were not exactly identical on matching variables (birth year, gender, MCO) because we did not always get exactly 3 matched controls per case within each matching stratum.
↵a P for χ2 test of independence between row (characteristic of study participant) and column (ASD case versus control).
↵b Recruitment of controls lagged behind case-children so that controls could be recruited to match case-children who had agreed to participate within birth year, gender, and MCO matching strata. The lagged recruitment meant that controls were an average of 3 months older than case-children at the time of interview/assessment.