TABLE 1

Sample Characteristics

Maternal CharacteristicsMean, SD or Weighted %
Age (y)27.5, 5.0
Race or ethnicity, %
 White, non-Hispanic58.5
 Black, non-Hispanic13.1
 Hispanic22.5
 Asian3.5
 Other2.3
Marital status, %
 Married68.9
 Unmarried31.1
History of prenatal smoking, %
 No89.2
 Yes10.8
Duration of breastfeeding, %
 <1 mo31.2
 2–3 mo30.7
 4–6 mo25.2
 >6 mo12.9
Plurality, %
 Singleton97.1
 Twin2.8
 Multiple (≥3)0.1
Socioeconomic indicators calculated from measures of education and income at 9 mo
 Maternal education, %
  Less than high school20.8
  High school degree30.4
  Some college22.1
  Bachelor’s degree15.9
  Graduate school10.8
 Below poverty threshold (<185% federal poverty line), %47.0
 At or above poverty threshold (≥185% federal poverty line), %53.0
Parenting behavior, 9 mo
 Parental responsiveness34.5, 7.1
Parenting behavior, 24 mo
 Parental sensitivity4.79, 1.2
 Parental cognitive stimulation4.13, 1.5
Parenting behavior, preschool
 Parental emotional support4.5, 1.2
 Parental cognitive stimulation4.2, 1.0