Unadjusted and adjusted Cox PH regression models for RTI-related mortality at 31–364 days in England relative to Sweden in 2003–2012
| Model 1 | Model 2 | Model 3 | |
| Country | |||
| England | 1.52 (1.26 to 1.82) | 1.16 (0.96 to 1.40) | 1.11 (0.92 to 1.34) |
| Sweden (baseline) | 1 | 1 | 1 |
| Birth weight (g) | |||
| 500–1499 | 5.94 (3.97 to 8.89) | 5.30 (3.54 to 7.94) | |
| 1500–2499 | 5.98 (4.59 to 7.79) | 5.38 (4.13 to 7.02) | |
| 2500–3499 | 2.11 (1.75 to 2.53) | 2.00 (1.66 to 2.41) | |
| ≥3500 (baseline) | 1 | 1 | |
| Gestational age (weeks) | |||
| 24–34 | 1.18 (0.86 to 1.61) | 1.23 (0.90 to 1.68) | |
| 35–36 | 1.29 (0.98 to 1.68) | 1.32 (1.01 to 1.72) | |
| 37–38 | 1.20 (1.01 to 1.43) | 1.21 (1.02 to 1.44) | |
| ≥39 (baseline) | 1 | 1 | |
| Sex | |||
| Boy | 1.05 (0.92 to 1.20) | 1.04 (0.91 to 1.19) | |
| Girl (baseline) | 1 | 1 | |
| Congenital anomaly | |||
| Yes | 25.72 (22.34 to 29.61) | 25.55 (22.20 to 29.41) | |
| No (baseline) | 1 | 1 | |
| Maternal age (years) | |||
| <25 | 1.34 (1.12 to 1.62) | ||
| 25–29 | 1.24 (1.03 to 1.49) | ||
| 30–34 (baseline) | 1 | ||
| ≥35 | 1.14 (0.93 to 1.40) | ||
| Quintile of socioeconomic status | |||
| Q1: most deprived | 1.96 (1.56 to 2.47) | ||
| Q2 | 1.73 (1.36 to 2.19) | ||
| Q3 | 1.25 (0.97 to 1.62) | ||
| Q4 | 1.19 (0.91 to 1.54) | ||
| Q5: least deprived (baseline) | 1 | ||
Data are adjusted HR with 95% CI. Each column represents a separate Cox PH model: model 1 was only adjusted for indicator of country with Sweden as baseline, model 2 was additionally adjusted for birth characteristics (birth weight, gestational age and presence of congenital anomalies), and model 3 was further adjusted for socioeconomic factors (socioeconomic status and maternal age).
PH, proportional hazards; RTI, respiratory tract infection.