General linear models for listed dependent variables: dependent variables were entered as the square root of the index variable to ensure residuals in the model were normally distributed
| Dependent variable | Factors/co-variates | Regression coefficients (95% CI) | p Value |
| Hospital admission in 12 months prior to clinical assessment | Unscheduled visits in prior 12 months | 0.051 (0.033 to 0.071) | p<0.001 |
| Total number of prior intensive care admissions | 0.086 (0.012 to 0.16) | p<0.05 | |
| Hospital centre | Belfast −0.108 (−0.341 to 0.126) | p<0.001 | |
| Brompton 0.418 (0.187 to 0.650) | |||
| Leicester 0.077 (−0.160 to 0.314) | |||
| Manchester 0 | |||
| On theophylline at initial assessment | 0.192 (0.017 to 0.366) | p<0.05 | |
| Rescue steroids in 12 months prior to clinical assessment | Hospital centre | Belfast 0.588 (0.295 to 0.881) | p<0.001 |
| Brompton 0.784 (0.490 to 1.078) | |||
| Leicester 0.757 (0.458 to 1.055) | |||
| Manchester 0 | |||
| Blood eosinophils at first assessment | 0.238 (0.105 to 0.372) | p<0.001 | |
| Age at first assessment at Difficult Asthma Service | −0.001 (−0.019 to −0.003) | p<0.01 | |
| Nebuliser usage at initial assessment | 0.223 (0.004 to 0.443) | p<0.05 | |
| Unscheduled visits in 12 months prior to clinical assessment | Age at first assessment at difficult asthma service | −0.011 (−0.019 to −0.003) | p<0.01 |
| Hospital centre | Belfast 0.500 (0.188 to 0.813) | p<0.01 | |
| Brompton 0.148 (−0.159 to 0.454) | |||
| Leicester 0.418 (−0.090 to 0.746) | |||
| Manchester 0 | |||
| Gender | 0.284 (0.051 to 0.518) | p<0.05 | |
| Blood eosinophils at first assessment | 0.147 (0.003 to 0.290) | p<0.05 |