Study design and study population

The design of this study has been previously described in Böhmer et al. 2016 (22). In short the current study is based on data collected for a prospective patient cohort study investigating the influence of beliefs about medicines on adherence in patients with asthma or COPD. For the study presented here only patients with COPD are investigated. In order to cover a broad range of disease severity, patients were recruited from primary care and specialist practices as well as from in- and outpatients from hospital settings. The study sites are located in the region of Regensburg in the German federal state of Bavaria. The recruitment period for the baseline survey was from June 2013 until December 2014. Only patients who met the following inclusion criteria were enrolled in the study: COPD as main diagnosis ascertained by a physician, age ≥18 years; disease duration ≥3 months; no acute psychiatric/neurological disease (exception: depression or affective disorders) and sufficient knowledge of the German language. After a short introductory explanation all patients gave informed consent on-site before filling in the questionnaire. Data was collected both by using validated instruments and information from the patients’ medical records. Based on previous studies we determined a priori that we would investigate variables belonging to the domains patient characteristics, disease characteristics, treatment-related factors and psychological characteristics, as we aimed to take a broad perspective on variables likely influencing HRQOL.