comScore study sheds new light on risks to cookie-based measurement
Published by Eric T. Peterson on April 16, 2007.
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Awhile back the folks at comScore called me and asked if I would be surprised to learn that cookies were being deleted at a pretty high rate. Of course I said, “No, because I reported as much in 2005.” Through the course of the conversation, however, it became clear that comScore had the ability to shed new light on our understanding of cookie-based measurement; specifically they had the ability to measure the rate of deletion associated with first-party cookies.
I will fight the temptation to smugly say, “Ah ha! I told you so …” since the comScore data shows that I was both right and wrong when I first wrote about cookie deletion when I was with JupiterResearch. I was right in my assessment that this is happening far more frequently than those of us in the web analytics field particularly want to believe. But I was wrong in my assumption that cookie deletion was largely limited to third-party cookies.
The comScore data reports that over 30 percent of their panel of 400,000 home user computers deleted both first- and third-party cookies. Now, when I talked to Andrew Lipsman and Gian Fulgoni from comScore I repeatedly encouraged them to check and double-check these findings since especially their number for first-party cookies is much, much higher than I think any of us expected to see.
That said, I have no reason to believe that comScore would make this claim frivolously (okay, except for the fact that they provide a competing methodology to cookies) … I have asked comScore for a deeper briefing on their research but nothing has been scheduled as of this posting. Perhaps on my urging comScore took their research a step further and surveyed a subset of their panel asking about their stated behavior towards cookies. In the press release, Dr. Magrid Abraham addresses this in the context of the conventional wisdom that assigns greater risk to third- than first-party cookies:
“There is a common perception that third-party cookie deletion rates should be significantly higher than first-party cookie deletion rates,” continued Dr. Abraham. “Because many PC users reset or delete their cookies using security protection programs, conventional wisdom dictates that people are more likely to selectively expunge third-party cookies – which are generally deemed more invasive – while maintaining their first-party cookies. But these findings suggest that selective cookie management is not prevalent, a fact that comScore confirmed via a survey, with only 4 percent of Internet users indicating that they delete third-party but not first-party cookies.”
Yikes. When you look at the tables in the comScore study you can see where the problem is coming from: serial cookie deleters, the 7% of site visitors (measured via the comScore panel) that are repeatedly removing their cookies and thusly will appear as a new site visitor with every visit. I addressed the idea of serial deleters in my final JupiterResearch report on “The Crumbling Cookie” and, at the time speculated that some of the more nefarious activities available through the Internet were to blame.
Still, I never would have put the number as high as 7 percent.
It’s interesting to me that cookies are back in the news. It will be more interesting to see how all of this is digested in the coming days, weeks, and months. I wonder if Seth Godin will comment on the comScore study? I mean, I’m not sure that the “echo chamber” argument applies to comScore’s panel of 400,000 measured, identified individuals.
This seems to be a topic ripe for commentary and conversation. What do you think? Is comScore crazy? Is this report flawed? Or are we just fooling ourselves when we believe that “unique visitor” counts are an accurate representation of the number of real human beings coming to our web sites over long periods of time?
About Eric T. Peterson
Eric T. Peterson is the founder of Web Analytics Demystified, Inc. and the author of Web Analytics Demystified, Web Site Measurement Hacks, and The Big Book of Key Performance Indicators. Mr. Peterson frequently presents on web analytics, is often cited in articles about digital measurement, and has been blogging on the subject since 2004.
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