The investigators will use a common-protocol approach to conduct retrospective cohort studies using health care data from eight jurisdictions (the Canadian provinces of Alberta, British Columbia, Manitoba, Nova Scotia, Ontario, Quebec, and Saskatchewan, as well as the United Kingdom (UK) Clinical Practice Research Datalink [CPRD]). The Canadian databases contain population-level data on physician billing, diagnoses and procedures from hospital discharge abstracts, vital statistics, and dispensations for prescription drugs. The CPRD is a clinical database that is representative of the UK population and contains the records for patients seen at over 680 general practitioner practices in the UK; these data will be linked to the Hospital Episode Statistics (HES) database, which contains in-hospital diagnosis and procedure data.