Crude risk ratios (RR) of developing two or more respiratory symptoms according to decreasing degree of AHR compared with subjects with PC20 >32 mg/ml
| Airway responsiveness (PC20) threshold values(mg/ml) | Cumulative† | |
|---|---|---|
| Subjects with incident respiratory symptoms n (%) | RR (95% CI) | |
| AHR, airway hyperresponsiveness; PC20, concentration of methacholine provoking a 20% fall in FEV1; RR, risk ratio; CI, confidence interval. | ||
| ***p<0.001; subjects with PC20 >32 mg/ml considered as reference category. | ||
| †p<0.001 for whole group (Cochran-Armitage tests for trend in RR applied to mutually exclusive categories of AHR). | ||
| ⩽4 | 9 (47.4) | 30.4 (9.9 to 93.0)*** |
| ⩽8 | 13 (34.2) | 17.6 (6.8 to 45.1)*** |
| ⩽16 | 27 (36.5) | 19.4 (8.6 to 43.8)*** |
| ⩽32 | 35 (30.4) | 14.8 (6.8 to 32.0)*** |
| >32 | 9 (2.9) | 1 |