Multivariable negative binomial regression model for acute respiratory tract infection events
| Characteristic | Event rate ratio (ERR (95% CI)) | |
| Primary model (prespecified) | Post hoc analysis | |
| Time (per year increase) | 1.01 (1.01 to 1.01) | 0.99 (0.99 to 1.00) |
| Smoke-free legislation | 1.24 (1.20 to 1.28)* | Dropped from model based on AIC |
| Time since smoke-free legislation (per year increase) | 1.06 (1.05 to 1.06)* | 0.91 (0.87 to 0.96)* |
| November 2004 break point | Not in model | 1.13 (1.08 to 1.19) |
| Time since November 2004 break point (per year increase) | Not in model | 1.16 (1.12 to 1.20) |
| Month (reference=January) | ||
| February | 0.83 (0.80 to 0.86) | 0.83 (0.80 to 0.86) |
| March | 0.78 (0.75 to 0.81) | 0.78 (0.75 to 0.81) |
| April | 0.54 (0.52 to 0.56) | 0.54 (0.52 to 0.57) |
| May | 0.52 (0.50 to 0.54) | 0.52 (0.50 to 0.54) |
| June | 0.46 (0.44 to 0.48) | 0.46 (0.44 to 0.48) |
| July | 0.33 (0.32 to 0.30) | 0.33 (0.32 to 0.35) |
| August | 0.29 (0.28 to 0.48) | 0.29 (0.28 to 0.31) |
| September | 0.47 (0.45 to 0.34) | 0.47 (0.45 to 0.49) |
| October | 0.57 (0.55 to 0.59) | 0.57 (0.55 to 0.60) |
| November | 0.84 (0.81 to 0.88) | 0.85 (0.82 to 0.88) |
| December | 1.26 (1.22 to 1.31) | 1.27 (1.23 to 1.32) |
| Male sex (reference=female) | 1.31 (1.28 to 1.33) | 1.31 (1.28 to 1.33) |
| Age 5–12 years (reference=0–4 years) | 0.07 (0.07 to 0.08) | 0.07 (0.07 to 0.08) |
| Region (reference=North) | ||
| South-West | 0.87 (0.85 to 0.89) | 0.87 (0.85 to0.89) |
| South-East | 0.90 (0.89 to 0.92) | 0.90 (0.89 to 0.92) |
| Living in urban area (reference=rural) | 0.99 (0.97 to 1.01) | 0.99 (0.98 to 1.01) |
| Socioeconomic status (reference=quintile 1; most affluent) | ||
| Quintile 2 | 1.11 (1.09 to 1.14) | 1.11 (1.08 to 1.14) |
| Quintile 3 | 1.14 (1.11 to 1.17) | 1.14 (1.11 to 1.17) |
| Quintile 4 | 1.25 (1.22 to 1.29) | 1.25 (1.22 to 1.29) |
| Quintile 5 (most deprived) | 1.35 (1.32 to 1.39) | 1.35 (1.31 to 1.39) |
| PCV vaccination received (reference=not received) | 0.45 (0.43 to 0.46) | 0.45 (0.43 to 0.46) |
| November 2003 (outlier) | 1.48 (1.37 to 1.60) | 1.61 (1.49 to 1.74) |
The post hoc analysis includes adjustment for an additional break point in November 2004.
*p<0.001 (p value only indicated for smoke-free legislation indicators).
AIC, Akaike’s information criterion; PCV, pneumococcal conjugate vaccine.