Unique Visitors - Everything You Know is Wrong

I've known this for 8 years or more, the way that most log analysis tools collects "unique users" is wrong. But Marketing wants that information so badly, that even if it's wrong, it's still data.

A study was done to compare if signed in (thus verifiably unique) users were similar in number to IP and cookie-based numbers. "The results are staggering: the IP-based approach overestimated unique users by 7.6 times, whilst a cookie-based approach overestimated unique users by 2.3 times."
Everything you know is wrong Note: you have to create an account to read this entire article.