Table 1.

Description of the type of data collected and stored in the national databases in Wales that were used in the data linkage in this study

National data source in Wales	Overview
Choose Pharmacy	A national web-based application that supports the delivery of NHS advanced and enhanced community pharmacy services in Wales. Holds data for all services completed in the pharmacy in the form of clinical information and predefined answers, including data for all electronic DMRs that were completed using Choose Pharmacy.
Patient Episode Database for Wales	A system that records all episodes of inpatient and day case activity in NHS Wales hospitals, which include planned and emergency admissions, minor and major operations, and hospital stays for giving birth.
Admitted Patient Care Data Set	Captures data for all consultant-led admitted patient activity, regardless of the patient’s area of residence. NHS Digital provides data on Welsh resident or registered patients treated in English NHS organisations. Once admitted, a patient may have several episodes within a hospital stay. Only once an episode is complete or the hospital spell ends will it be captured in the Admitted Patient Care Data Set.
Office of National Statistics death notifications database	Annual data on deaths registered by age, sex and selected underlying cause of death.
Welsh Demographics Service	Provides the demographic characteristics of people registered with GP practices in Wales. The Welsh Demographics Service maintains a register of Welsh residents’ demographic details, including name, address, date of birth, general practice and NHS number. For any consultations completed via Choose Pharmacy, patients are linked to the Welsh Demographic Service and matched to existing health records, enabling collection of demographic information.
National Data Resource	A resource currently being developed to better enable NHS Wales to improve patient experience and service outcomes. The National Data Resource aims to deliver a more joined-up approach to health and care data, using common language and technical standards and providing improved analytics capability.

DMRs, discharge medicines reviews; GP, general practitioner; NHS, National Health Service.