Anne Holland

New Data: 40% of consumers zap cookies weekly — popular sites' monthly uniques may be inflated

April 22nd, 2004

If you’re an online ad media buyer, an e-retailer concerned with conversion data, or anyone else who analyzes site stats for a living, unique visitor counts are a critical metric.

However, various adware-zapping programs are putting your stats in danger.

Greg Harmon of Belden Associates who’s run readership surveys for more than 40 US newspaper sites told me he began to wonder why nearly every single site’s log files only showed three average visits per user per month when, according to nearly 70,000 survey answers, on average readers visit a particular newspaper site 24 times per month.

If true, the discrepancy meant only 20% of the uniques the log files reported were actually uniques. The rest were repeat visitors who mysteriously appeared to be newbies.

People switching between work and home computers accounted for about 25% of the discrepancy … not enough to be the main answer.

So, 60 days ago Greg decided to add two questions to surveys he was running for three newspapers — one in Virginia, one in Illinois and one in California. Figuring that adware-stopper downloads are now probably in the hundreds of millions, He asked survey takers how often they cleared their cookies.

Of 3,500 answers, about 40% said they cleared cookies at least once a week. And, these weren’t geeks. The median age was 40, and 2/3 were women.

Greg is putting together a PDF with some initial data on this. It will be ready Monday, and he told me you can get it by emailing him at

I also called up David Barlin over at I/PRO who conduct site traffic audits. He told me he agrees, you should never rely on site log counts to determine true uniques, especially if you’re a media buyer fretting about reach and frequency. I/PRO has developed an algorithm to run against reported site stats to determine true traffic. Interesting…

So, annoyingly, the world’s most measurable advertising medium is now, thanks to increased cookie-wiping, harder to measure remotely accurately.

Useful links related to this Blog:

Interesting article in Editor & Publisher on Belden’s data:

I/PRO & BPA Int’l info on the new Agencies for Interactive Audits program:

Belden Associates

Permanent link to this Blog column on our site:

Categories: Uncategorized Tags:

We no longer accept comments on the MarketingSherpa blog, but we'd love to hear what you've learned about customer-first marketing. Send us a Letter to the Editor to share your story.