NNT to prevent a COPD exacerbation over different 6-month periods during follow-up from the TORCH trial of fluticasone/salmeterol compared with placebo [4]
| Period of follow-up | COPD exacerbations per patient per 6-month period | NNT | |
| Fluticasone/salmeterol | Placebo | ||
| First year | |||
| First 6 months | 3.4 | 1.5 | 0.5 |
| Second 6 months | 1.1 | 0.85 | 4 |
| Second year | |||
| First 6 months | 0.85 | 0.65 | 5 |
| Second 6 months | 0.75 | 0.65 | 10 |
| Third year | |||
| First 6 months | 0.75 | 0.55 | 5 |
| Second 6 months | 0.45 | 0.40 | 20 |
NNT: number needed to treat; COPD: chronic obstructive pulmonary disease; TORCH: Towards a Revolution in COPD Health.