Nat. Biotechnol. 27, 3–5 (2009); published online 8 January 2009; corrected after print 9 February 2009

In the version of this article initially published, we neglected to define our categories for public biotech firms. In the following definitions, the dollar amounts refer to a firm's market capitalization or 'cap': microcap, <$250 million; small cap, $250 million to <$1 billion; mid-cap, $1 billion to <$5 billion; large cap, ≥$5 billion. The definitions have been added to Box 2, Figure 1 legend, in the HTML and PDF versions of the article.