Table 1.
Descriptive Statistics
| N | Mean (SD) | Range | Frequency (%) |
|
|---|---|---|---|---|
|
| ||||
| IPI | ||||
|
| ||||
| Short IPI (≤ 1 year) | 5339 | – | – | 1171 (22) |
| IPI reference (>1 year, ≤ 3 years) | 5339 | – | – | 2228 (42) |
| Long IPI (> 3 years) | 5339 | – | – | 1940 (36) |
| IPI (in years) | 5339 | 2.99 (2.78) | 0.01,26.57 | – |
|
| ||||
| Covariates | ||||
|
| ||||
| Female child | 5339 | – | – | 2599 (49) |
| Birth order | ||||
| Second | 5339 | – | – | 3204 (60) |
| Third | 5339 | – | – | 1474 (28) |
| Fourth | 5339 | – | – | 493 (9) |
| Fifth | 5339 | – | – | 168 (3) |
| Race | ||||
| White | 5339 | – | – | 2736 (51) |
| Hispanic | 5339 | – | – | 1069 (20) |
| African American | 5339 | – | – | 1534 (29) |
| Maternal age at childbearing | ||||
| < 20 years | 5339 | – | – | 432 (8) |
| 20 to 24 years | 5339 | – | – | 1732 (32) |
| 25 to 29 years | 5339 | – | – | 1799 (33) |
| 30 to 34 years | 5339 | – | – | 956 (18) |
| ≥ 35 years | 5339 | – | – | 420 (8) |
| Years of maternal education | 5335 | 12.83 (2.65) | 1.00,20.00 | – |
| Maternal IQ | 5073 | 0.00 (1.00) | −1.22,2.43 | – |
| Maternal depression | 4413 | 0.00 (1.00) | −1.11,4.63 | – |
| Maternal lifetime alcohol problems | 4392 | 1.68 (3.30) | 0.00,25.00 | – |
| Maternal delinquency | 5041 | 0.00 (1.00) | −1.04,6.20 | – |
| Family income (square root) | 4553 | 0.00 (1.00) | −1.68,9.43 | – |
| Half-siblings in family | 5339 | – | – | 2271 (43) |
| Miscarriage, stillbirth, or abortion during IPI | 5339 | – | – | 612 (11) |
|
| ||||
| Outcomes | ||||
|
| ||||
| Birth outcomes | ||||
| Birth weight (in grams) | 5060 | 3344.67(615.35) | 453.60,7597.80 | – |
| Gestational age (in weeks) | 5339 | 38.56 (2.14) | 23.00,49.00 | – |
| Preterm birth | 5339 | – | – | 632 (12) |
| Infant temperament | ||||
| Activity | 1447 | 0.00 (1.00) | −1.77,1.90 | – |
| Predictability | 1442 | 0.00 (1.00) | −4.10,0.96 | – |
| Fearfulness | 3021 | 0.00 (1.00) | −1.27,2.80 | – |
| Positive affect | 3009 | 0.00 (1.00) | −4.07,0.83 | – |
| Fussiness | 3024 | 0.00 (1.00) | −1.60,4.29 | – |
| Child cognitive ability | ||||
| Digit span | 3636 | 0.00 (1.00) | −2.90,3.14 | – |
| PPVS | 3270 | 0.00 (1.00) | −3.49,3.43 | – |
| Math | 3768 | 0.00 (1.00) | −2.50,2.44 | – |
| Reading recognition | 3766 | 0.00 (1.00) | −2.47,2.22 | – |
| Reading | 3740 | 0.00 (1.00) | −6.09,2.75 | – |
| Child externalizing problems | ||||
| Conduct | 4517 | 0.00 (1.00) | −1.17,12.22 | – |
| Oppositional Defiant | 4515 | 0.00 (1.00) | −1.27,3.17 | – |
| Attention-Deficit/Hyperactivity | 4515 | 0.00 (1.00) | −1.23,3.15 | – |
Note: IPI = interpregnancy interval. SD = standard deviation. Number of years of maternal education was assessed in 2012. Maternal IQ was assessed in 1980. Maternal depression was assessed in 1992. Maternal alcohol use and dependence symptoms were assessed in 1994. Maternal delinquency was evaluated for maternal ages 15 to 22 years. Family income was reported by mothers when they were 30 years old. Infant temperament was evaluated between birth and 23 months. The child cognitive ability measures were based on biennial assessments between ages 9 and 12 years. The child externalizing problem measures were based on biennial assessments between ages 4 and 9 years.