Investigators are building an empirical evidence base for real world data through large-scale replication of randomized controlled trials. The investigators' goal is to understand for what types of clinical questions real world data analyses can be conducted with confidence and how to implement such studies.

This is a non-randomized, non-interventional study that is part of the RCT DUPLICATE initiative (www.rctduplicate.org) of the Brigham and Women's Hospital, Harvard Medical School. It is intended to replicate, as closely as is possible in healthcare insurance claims data, the trial listed below/above. Although many features of the trial cannot be directly replicated in healthcare claims, key design features, including outcomes, exposures, and inclusion/exclusion criteria, were selected to proxy those features from the trial. Randomization is also not replicable in healthcare claims data but was proxied through a statistical balancing of measured covariates according to standard practice. Investigators assume that the RCT provides the reference standard treatment effect estimate and that failure to replicate RCT findings is indicative of the inadequacy of the healthcare claims data for replication for a range of possible reasons and does not provide information on the validity of the original RCT finding.

Inclusion Criteria:

• Age between 40-80 years [0,0] days
• Diagnosis of COPD [all available data, 0] days
• Clinical history of at least 1 COPD exacerbation [all available data, -43] days

Exclusion Criteria:

• COPD exacerbation [-42, 0] days
• Asthma, eczema, atopic dermatitis, allergic rhinitis [-180, 0] days
• Known respiratory disorder other than COPD e.g. pulmonary fibrosis or interstitial lung disease (ILD), sarcoidosis, lymphangioleiomyomatosis, primary/pulmonary tuberculosis, cystic fibrosis, pulmonary hypertension/other pulmonary heart disease, lung/pulmonary malignancies, alpha-1 antitrypsin deficiency, pneumoconioses and other lung diseases due to external agents [all available data, 0] days
• Narrow angle glaucoma or prostatic hyperplasia or obstruction of the neck of the bladder [-180, 0] days
• At least one 30-day supply prescription claims for oral alfuzosin, doxazosin, tamsulosin, silodosin, finasteride 5 mg, dutasteride [-180,0] days
• Lung transplant or lung volume reduction surgery (LVRS) [all available data, 0] days
• Daily long term oxygen therapy (LTOT) [all available data, 0] days
• Beta-blockers (except eye drops) [-180, 0] days
• Evidence of alcohol, drug or solvent abuse [-180, 0] days
• Use of salmeterol, tiotropium and fluticasone containing inhaler use [-180, 0] days

This study will involve a new user, parallel group, propensity score matched retrospective cohort study design comparing tiotropium to salmeterol. The patients will be required to have continuous enrollment during baseline period of 180 days before initiation of SFC or tiotropium inhalers (cohort entry date).