Table 2.

Confounding Variables Used in Multivariate Analysis

Infants’s age
 2, 3, 4, 5, 6, 7, 9, and 12 mo
Infant’s gender
 F
 M
Mother’s education
 0–11 y of school
 12 y of school
 1–4 y of college
 >4 y of college
Mother’s occupation
 Full-time homemaker
 Unemployed, student, or retired
 Professional or executive
 Clerical or sales
 Craftsman, fabricator, technician, farmer, service worker, etc
Mother’s smoking
 No smoking
 ≤10 cigarettes/day
 11–20 cigarettes/day
 >20 cigarettes/day
Household size
 1–2 people
 3 people
 4–8 people
Household Income
 <$22 500
 $22 500–$34 999
 $35 000–$50 000
 >$50 000
Day care
 No care
 1–2 days/wk
 3–5 days/wk
 6–7 days/wk