Stack Exchange sites use Quantcast, which collects demographic data (by redirecting some percentage of traffic to an anonymous beacon, such as Facebook's, which matches the visitor to the data that Facebook's beacon discloses about them.) Or at least used to collect, as a post by an SE employeepost by an SE employee ends with "we appreciate the ability to opt out of the beacon and plan on turning it off". In any case, Quantcast's demographic card for Ask Ubuntu has
- Male: index 191
- Female: index 13
indicating that a randomly chosen visitor to AU is 91% more likely to be male than a random Internet user (and 87% less likely to be female). Take the data with a generous helping of salt, but that's all we have.