Table 2.
Demographic characteristics
| Variable | Mean±SD/Number (Percent) | # Obs. | % Missing |
|---|---|---|---|
| Gestational age (weeks) | 31.3±3.3 | 688 | 0.1 |
| Birth weight (grams) | 1,767±719 | 689 | 0.0 |
| Infant gender (Male) | 380 (55.2%) | 689 | 0.0 |
| Infant race (Caucasian) | 592 (87.8) | 674 | 2.2 |
| Twin/multiple | 130 (18.9%) | 689 | 0.0 |
| Season of birth | 689 | 0.0% | |
| Winter (Dec–Feb) | 197 (28.6%) | ||
| Spring (Mar–May) | 141 (20.5%) | ||
| Summer (Jun–Aug) | 164 (23.8%) | ||
| Fall (Sep–Nov) | 187 (27.1%) | ||
| Age (hours) at time of sample collection | 29.3±6.9 | 689 | 0.0 |
| APGAR score at 1 minute | 6.2±2.1 | 681 | 1.2 |
| APGAR score at 5 minutes | 7.9±1.3 | 682 | 1.0 |
| Highest total bilirubin (mg/dL) | 9.5±3.1 | 646 | 6.2 |
| Respiratory distress syndrome (RDS) | 364 (60.6%) | 601 | 12.8 |
| Patent ductus arteriosus (PDA) | 133 (19.9%) | 669 | 2.9 |
| Necrotizing enterocolitis (NEC) | 12 (2.0%) | 611 | 11.3 |
| Congenital anomaly | 50 (7.3%) | 689 | 0.0 |
The number of observations represents the total number of individuals with non-missing data for a given variable.