I don't think the ratio is that low. Probably closer to 20:1

There was one poster that I respected and assumed was male. One day, they posted links to feminist blog posts that they had obviously book-marked (They were not recent). I am not saying men can't read feminist blogs (I do myself on occasion); but from that point on, I "read" them as female.

I think my point is that for every woman than announces their gender, there are probably about 10 that stay "stealth".