The dataset currently contains (1) a table of time periods (defined with start and end dates) during which a patient had any diagnosis of asthma; (2) and table of time periods for asthma severity level (based on prescriptions), asthma exacerbations, asthma-related hospital episodes, and asthma control; and (3) a table for other asthma-related data represented as events (e.g., lung function, blood tests, and A&E visit).

Includes an e-cohort of most people with a history of asthma in Wales, derived from the SAIL Databank's core datasets. Individuals are identified from the Welsh Longitudinal General Practice (WLGP) using several case definitions (e.g., having ever GP asthma diagnosis, asthma treatment in the last 12 months, or both). Data for each patient include essential research-ready asthma-related variables derived from primary and secondary care data, such as asthma treatment step, asthma severity, asthma exacerbations, and asthma-related death. The case definitions and some clinical variables are represented as clinical states. Additional case definitions and variables are actively being added. The WAO dataset is intended to support a wide range of cross-sectional and longitudinal epidemiological asthma studies as well as asthma surveillance, service planning, and health policy.