Observational studies of inhaled corticosteroids in chronic obstructive pulmonary disease
(COPD) have shown improved survival whereas randomized trials have not. It has been
suggested that this difference may be due to immortal time bias. To investigate this further,
we performed a prospective cohort study of patients with COPD, using time-dependent
methods to determine whether use of inhaled corticosteroids more than 80% of the time
reduced the risk of all-cause mortality and COPD exacerbations. Of 8,033 patients, 2,686 …

The effectiveness of inhaled corticosteroids (ICS) in patients with chronic obstructive
pulmonary disease (COPD) remains controversial. Randomized controlled trials, meta-
analyses, medication withdrawal studies, and observational reports have examined this
question, with mixed results. Observational studies have been subject to criticism because of
study design involving immortal time bias. Some randomized controlled trials suggest small
benefits in lung function and health status, and a reduction in the rate of acute exacerbations …