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

In the version of this article initially published, funding information for L.P. was omitted. The author acknowledges funding from the German Federal Ministry of Education and Research (0315893B/Sybacol (Systems Biology of Ageing Cologne)). The error has been corrected in the HTML and PDF versions of the article.