TY - JOUR T1 - Avoiding immortal time bias in observational studies JF - European Respiratory Journal JO - Eur Respir J DO - 10.1183/13993003.02494-2019 VL - 55 IS - 3 SP - 1902494 AU - Adam J.N. Raymakers AU - Mohsen Sadatsafavi AU - Don D. Sin AU - J. Mark FitzGerald AU - Carlo A. Marra AU - Larry D. Lynd Y1 - 2020/03/01 UR - http://erj.ersjournals.com/content/55/3/1902494.abstract N2 - We read with interest the recent study by Suissa et al. [1] published in the European Respiratory Journal. The study used population-based administrative data from the province of Quebec, Canada, to evaluate the association between inhaled corticosteroid (ICS) exposure and lung cancer risk in patients with COPD. The results of the study indicated that ICS use was not associated with lung cancer risk in this patient population.Immortal time bias is common in observational studies; however, in the analysis conducted by Raymakers and colleagues appropriate measures were taken to avoid this bias http://bit.ly/36042OV ER -