<qa>  What is the CPRD?A common-protocol approach will be used to conduct retrospective cohort studies using administrative health care data from eight jurisdictions the Canadian provinces of Alberta, Manitoba, Nova Scotia, Ontario, Quebec, Saskatchewan, as well as the United Kingdon UK Clinical Practice Research Datalink and the United States US Marketscan. Briefly, the Canadian databases include population-level data on physician billing, diagnoses and procedures from hospital discharge abstracts, and dispensations for prescription drugs. The data in Nova Scotia, Ontario, and Alberta will be restricted to patients aged 65 years and older, as prescription data are not available for younger patients. 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. 