Nat. Methods 11, 100–105 (2014); published online 17 November 2013; corrected after print 8 August 2014; corrected after print 19 October 2015

In the version of this article initially published, only one corresponding author was listed (M.D.W.P.). L.P. has been added as a corresponding author for this article. The relevant contact information is partridge@age.mpg.de. This information has been added to the HTML and PDF versions of the article.