One of the largest big-data experiments in health care has set its first research target. The leaders of the Patient-Centered Outcomes Research Institute (PCORI) in Washington DC voted on 29 July to focus the institute’s first clinical trial on the use of aspirin to prevent heart disease. The US$10-million pilot study will be conducted through PCORnet, a network set up by PCORI to collect health-care data such as insurance claims, blood tests and medical histories for as many as 30 million people in the United States.