It is a limitation in this study that surrogate measures are used to define chronic cough, both from the Prescription database and the Patient registry, even though measures were taken to eliminate reasons for acute cough through exclusion of antibiotics, cough due to ACE-inhibitors and diagnosed cancers as well as not having the exact time frame of the cough prior to final diagnosis in the Patient registry, even though in the Danish clinical setting the final diagnosis can be defined as a contact lasting for ≥8 weeks. This evidence concerns the gene ACE and cancer.