Last Updated Apr 16, 2010 2:12 PM EDT
"Studies looking specifically at the consequences of appointing women to corporate directorships show that stock performance tends to be unchanged or slightly worse after boards increase their gender diversity," writes Andrew O'Connell.
Why? Bias held by small-share investors, who are for some reason made nervous by the growing diversity on the board and sell, driving the price down. Investors who hold large blocks of stock actually buy more shares, but not enough to counter the smalls.