Source: http://www.nytimes.com/2016/01/10/upshot...

Here is where it gets interesting. When an economist writes a paper on her own, there is no question about who deserves the credit. Each additional solo research paper raises the probability of getting tenure by about 8 or 9 percent, she calculated. The career benefit from publishing a solo paper is about the same for women as it is for men. But unlike women, men also get just as much credit for collaborative research, and there is no statistical difference in the career prospects of authors of individually written papers and those of papers written as part of a research team.

Unfortunately for women, research done with a co-author counts far less. When women write with co-authors, the benefit to their career prospects is much less than half that accorded to men. This really matters, because most economic research is done with co-authors.