What is the effect of a journal going open-access on its impact factor? I recently saw this reasonably interesting graphic regarding journals and open access.



As many of you know, there is a large discussion about open access. It appears to be most strong within biological sciences, though that may be more of a side-effect of their style of publishing. An interesting "timeline of open access" unfortunately stops at 2008. Obviously the graphic, while interesting, is a single data point.

What is the evidence regarding the effect of going open-access and a journal's impact factor? I am especially interested in utilizing resources that have undergone some kind of peer review and scrutiny.
A few years ago there appeared a nice article in Science:

Open Access and Global Participation in Science

The authors convincingly show that going Open Access widens the readership of journals and improves citation counts.

There are some interesting references in that article too.