Wow, I just downloaded a great report from ComScore on the effect of cookie deletion on our user statistics. Unbelievable.
They estimate the following:
- 30% of computer users clear out their cookies monthly
- 12% of computers are set to reject cookies
- An average of 2.5 distinct first party cookies were observed per computer per site
What does this all mean?
It means that our unique visitor figures are overstated by, now are you ready, 150%. In other words, those 1000 unique visitors are more like 400.
And, the number is even worse for third party cookies.
Please go to ComScore and download their free whitepaper. It is extremely well written and explains all the issues. For my web analytics students this is a must read.