I've been gaming for over 30 years now, and have only gamed with 3 women in that time, with one more coming up (a guy in my group is having his g/f join, but she is replacing the woman who dropped out because she is divorcing one of the guys in my group... )
So, I would say that would be 4 women out of well over 100 gamers. So, maybe 1:30?
This has all been private gaming - I have never been to any sort of gaming convention anywhere.
The three married guys in our group (me included) all have non gaming wives.