It’s hard to pinpoint the exact reason for the gap. But economics may be slower to integrate because women may not be comfortable with its “aggressive style,” according to Heidi Hartmann, the president of the Institute for Women’s Policy Research.

“When a field is dominated by men and it is characterized by aggression, that can be a double reason why women don’t want to do it, because they’re not really socialized to be aggressive, and they see mostly men,” Hartmann said.

Women are often intimidated by the “macho sense of competition” in economics, where people are quick to “pounce” on wrong ideas, making them less likely to speak up, according to Kahn, one of the authors of the 2004 study. Even when women do share their ideas, they don’t always get credit, she said.