Asthma contacts: factors exerting statistically significant independent effects
| Signifiicant factors | n | IRR | 95% CI | p value |
| Age of child (years) | ||||
| 2–3 | 49 | 1.00 | – | |
| 4 | 44 | 0.77 | 0.63 to 0.94 | 0.012 |
| 5–7 | 147 | 0.64 | 0.54 to 0.75 | <0.0001 |
| 8–10 | 129 | 0.49 | 0.41 to 0.59 | <0.0001 |
| 11–12 | 69 | 0.41 | 0.33 to 0.51 | <0.0001 |
| Perceived severity of asthma | ||||
| Very mild | 95 | 1.00 | – | – |
| Mild | 181 | 1.08 | 0.92 to 1.27 | 0.36 |
| Moderate | 128 | 1.34 | 1.13 to 1.58 | 0.001 |
| Severe | 28 | 1.49 | 1.17 to 1.89 | 0.001 |
| Very severe | 6 | 2.68 | 1.94 to 3.70 | <0.0001 |
| Severity of asthma by BTS step | ||||
| Step 1 | 83 | 1.00 | – | – |
| Step 2 | 49 | 1.94 | 1.52 to 2.46 | <0.0001 |
| Step 3 | 272 | 2.01 | 1.67 to 2.42 | <0.0001 |
| Step 4 & 5 | 34 | 2.40 | 1.89 to 3.06 | <0.0001 |
| No of parents who smoke | ||||
| Father only | 66 | 1.00 | – | – |
| Mother only | 194 | 0.76 | 0.64 to 0.89 | 0.001 |
| Both parents | 178 | 0.78 | 0.66 to 0.93 | 0.006 |
| No of children in family | ||||
| 1 | 92 | 1.00 | – | – |
| 2 | 208 | 0.99 | 0.85 to 1.14 | 0.86 |
| 3 | 92 | 0.84 | 0.71 to 1.00 | 0.05 |
| 4 or more | 46 | 0.74 | 0.59 to 0.93 | 0.01 |
| Child cotinine level | ||||
| Low | 135 | 1.00 | – | – |
| Medium | 153 | 0.95 | 0.82 to 1.11 | 0.52 |
| High | 150 | 1.15 | 0.98 to 1.34 | 0.08 |
IRR = the incidence rate ratio, the frequency of the number of contacts as a ratio of the frequency in the reference category (the first category of each factor).