Table 3. Pneumonia IRRs by age among 5204 children, adjusted for altitude, number of children under 36 months of age in household and gender, Punial and Ishkoman valleys, Pakistan, 1 November 2001 to 31 December 2002.
| Covariate | IRR | 95% CI |
|---|---|---|
| Age group, in months | ||
| Reference = 24–35 | ||
| 2 to < 6 | 4.33* | 3.53–5.32 |
| 6 to < 12 | 3.27* | 2.66–4.03 |
| 12 to < 18 | 2.69* | 2.18–3.32 |
| 18 to < 24 | 2.04* | 1.64–2.53 |
| Altitude range, in metres | ||
| Reference = 1675–1980 | ||
| 1980–2285 | 1.66* | 1.45–1.90 |
| 2286–2590 | 1.09 | 0.92–1.30 |
| > 2590 | 0.16* | 0.08–0.32 |
| No. of children < 36 months old in household | ||
| Reference = 0 | ||
| 1–2 | 0.99 | 0.84–1.17 |
| ≥3 | 1.03 | 0.78–1.35 |
| Gender | ||
| Reference = female | ||
| Male | 1.14* | 1.01–1.29 |
CI, confidence interval; IRR, incidence rate ratio. * P < 0.05 in Poisson regression analysis.