I just happened to write my contact at comScore today asking about their follow-up report on cookie deletion. He said it would be out today and here it is:
This report does a good job of providing additional data and information about the comScore methodology in this report, something missing from the press release and critical to our collective understanding of cookie deletion. This report explicitly addresses anti-spyware and the differences in third- and first-party cookie deletion, essentially showing that there is an anti-spyware effect but it is minimal compared to manual cookie deletion which appears to be the primary culprit.
comScore also presents some of the attitudinal data they alluded to in their press release, essentially confirming what I first reported at JupiterResearch in 2005 … that most consumers aren’t really sure what cookies do.
Since I last saw the report they added a few sections — one on international traffic and one on cookie blocking. While the section on international doesn’t add much to the conversation other than to explain why panel-based and log-based systems numbers differ (something that should be fairly obvious), the cookie blocking data is pretty interesting.
According to comScore, if your web analytics application falls-back to an IP-based value for unique visitor identification in the absence of a cookie being successfully set, you’re likely worse off than you are simply dropping those visitors. Their table on page 15 shows that due to dynamic IP assignment that the average home computer has 10.5 different IP addresses in a month. Yikes!
If you’re into this stuff, or if you’re interested in how much cookie deletion might be impacting your own audience measurement, you should download the report and give it a careful read. It certainly doesn’t provide a solution to the problem, but often times knowing is half the battle.
I welcome your feedback on the report and the usual comments and criticism.