Data sources
All eight participating sites analysed data from their respective administrative healthcare databases, all of which have been used previously for observational research.9 10 All databases included information on the specific drug dispensed in a prescription, the quantity or days’ supply of medication dispensed (or prescribed in CPRD), and the date of dispensing. In general, physician claims and hospitalisation discharge records included date of service encounter or hospital admission, up to 25 ICD-9 or ICD-10 (international classification of diseases, ninth or 10th revision) diagnosis codes, and procedure and billing codes. Patients who were missing demographic data (sex,