Nat. Biotechnol. 33, 45–47 (2015); published online 9 January 2015; corrected after print 30 April 2015

In the version of this article initially published, the number of patients said to be included in the PRO-ACT database was given as 1,822. There are 8,635 patients in the database to date, of which 1,822 were included in the crowdsourcing challenge. The error has been corrected in the HTML and PDF versions of the article.