Following patients through different health and health care events often requires the linkage of patient records across databases. Record linkage involves linking two or more databases using a unique patient identifier. In 2012, 14 countries had national data containing identify ing information that could be used for record linkage for hospital inpatient data for example (OECD, 2013c). Only Australia, Germany, Poland and the United States did not report a unique identifying number within their national hospitalisation databases.