Where is the information about the methodology of the survey?

The submitted article says the "survey" is based on DoubleClick Ad Planner,

https://accounts.google.com/ServiceLogin?service=branding...

a Google service, but it's not explained how DoubleClick knows about (for example) users who habitually block cookies and the like, and anyway how does DoubleClick match its data sources with the overall population that uses Hacker News? What is the evidence that the headline figure is anything other than a wild-ass guess?