Limitations of the evidence suggesting that inhaled corticosteroids (ICS) and long-acting β-agonists (LABA)/ICS decrease exacerbations of chronic obstructive pulmonary disease
| Most trials do not follow patients for the outcome of exacerbations after drug discontinuation (not ITT) |
| Loss to follow-up frequent and related to both treatment received and outcome, causing bias |
| Exacerbations variably defined |
| Differences between groups possibly exaggerated by withdrawal of ICS in placebo and LABA groups |
| Incorrect calculation of NNT |
| Incorrect adjustment for heterogeneity of number of exacerbations between patients in early studies |
ITT: intention to treat; NNT: number needed to treat.