Managerial gender equity predicts ROI?

According to a study quoted in a recent New Scientist, the companies in the Fortune 500 with the highest number of women in senior management positions had 35% higher return on stockholder investment than those with the fewest. Sounds good, but be aware that the study was done by “Catalyst, a 'on-adversarial advocacy organization,'works to advance women in business leadership with a particular focus on placing women on the boards of Fortune 500 companies.”