"Self-reported"
OF COURSE we know that is the standard way, "We made no attempt to measure how accurately and honestly subjects filled out their demographic surveys."
Which is sad... Social numbers
It would not have been that hard to have people go directly to a survey, right from the phishing link :-)
Also, more details on the response? how long did it take those who reported to do so?
obligatory XKCD https://www.xkcd.com/435/
Biting the hand that feeds IT
