Nat. Biotechnol. 32, 750–751 (2014); published online 7 August 2014; corrected after print 8 August 2014; 10.1038/nbt.2962

In the version of this article initially published, in the last paragraph, the sentence beginning, “However, the authors demonstrate that,” should have ended with “...far fewer than the hundreds of samplings used here will suffice for many purposes.” Instead of “...far fewer than the hundred of reads used here will suffice for many purposes.” The error has been corrected in the HTML and PDF versions of the article.