Thank you, this cannot be said enough. About AppData, ComScore, Compete, or any other public traffic estimator.
I love AppData to pieces, it's fantastically useful and I hit it pretty much every day--but it doesn't actually even match Facebook's data sometimes and Facebook logins are only one of Quora's supported login types, so one could extrapolate that there are at least that many users but in no way could you say that's even close to the topline (you might guess it's 2/3 of it, but it'd still be a SWAG).
I love AppData to pieces, it's fantastically useful and I hit it pretty much every day--but it doesn't actually even match Facebook's data sometimes and Facebook logins are only one of Quora's supported login types, so one could extrapolate that there are at least that many users but in no way could you say that's even close to the topline (you might guess it's 2/3 of it, but it'd still be a SWAG).