Sensitivity analysis
| Parameter | New cases (per 100 targeted) | Rate difference (per 100 targeted) | % additional cases detected with active approach | NNT | Proportion of expected cases in the community detected with active approach | |
| Active | Opportunistic only | |||||
| Base case | 3.8 | 2.2 | 1.6 | 70% | 63 | 0.49 |
| Model assumptions | ||||||
| Proportion with any respiratory symptom | ||||||
| 0.3 | 2.4 | 1.4 | 1.0 | 70% | 101 | 0.49 |
| 0.7 | 5.5 | 3.2 | 2.3 | 70% | 45 | 0.49 |
| COPD* in those with respiratory symptoms | ||||||
| 0.1 | 2.4 | 1.4 | 1.0 | 70% | 101 | 0.49 |
| 0.2 | 4.7 | 2.8 | 2.0 | 70% | 50 | 0.49 |
| 0.3 | 7.1 | 4.1 | 3.0 | 70% | 34 | 0.49 |
| Process assumptions | ||||||
| Questionnaire response rate (postal) | ||||||
| 0.3 | 3.2 | 2.2 | 1.0 | 43% | 105 | 0.41 |
| 0.7 | 4.4 | 2.2 | 2.2 | 101% | 45 | 0.58 |
| GP asks questionnaire in surgery | ||||||
| 0.1 | 2.9 | 0.4 | 2.5 | 561% | 41 | 0.38 |
| 0.2 | 3.1 | 0.9 | 2.2 | 255% | 45 | 0.41 |
| 0.3 | 3.3 | 1.3 | 2.0 | 154% | 49 | 0.41 |
| 0.7 | 4.2 | 3.1 | 1.2 | 37% | 87 | 0.55 |
| Spirometry uptake rate | ||||||
| 0.5 | 2.7 | 1.6 | 1.1 | 70% | 88 | 0.35 |
| 0.9 | 4.9 | 2.8 | 2.0 | 70% | 49 | 0.63 |
| Spirometry accuracy | ||||||
| 0.9 sensitivity | 3.4 | 2.0 | 1.4 | 70% | 70 | 0.44 |
| 0.8 sensitivity | 3.0 | 1.8 | 1.3 | 70% | 79 | 0.39 |
Numbers in bold are referred to in the text.
↵* Clinically significant COPD defined as respiratory symptoms and airways obstruction (National Institute for Health and Clinical Excellence criteria).
COPD, chronic obstructive pulmonary disease; GP, general practitioner; NNT, number needed to target with the active approach to identify one additional new case over opportunistic only.