Acta Crystallographica – Section A came out of nowhere to knock the New England Journal of Medicine out of the #2 overall spot in this year’s 2009 ISI Impact Factors. How in the heck?

It turns out that one article on the development of SHELX, used for structure refinement in crystal structure determination, was cited more than 6600 times. For a journal that published 126 papers in the IF window, this increased the IF from 2.051 to 49.926.

The authors even suggested citing this paper in the abstract:

This paper could serve as a general literature citation when one or more of the open-source SHELX programs (and the Bruker AXS version SHELXTL) are employed in the course of a crystal-structure determination.

Remember, the Impact Factor is not a normal distribution, and will be sensitive to single papers like this.

The Scientist covered this story in New impact factors yield surprises, and ISI posted an explanation in their forums.