A Look at Google Ad Planner Data Vs. Comscore

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Exclusive: A Look at Google Ad Planner Data Vs. Comscore

from John Battelle's Searchblog

When Google Ad Planner came out back in June, I immediately thought of Comscore - and I was not alone. Many in the marketing industry thought that Google's product would be a "Comscore killer," and when I noted as much in my coverage, Gian Fulgoni, Comscore's chair, shot back in acomment to my post:

Hi John: Before celebrating the availability of these products from Google, I think it would be prudent for web site operators to compare their site traffic numbers as obtained from their server logs (or Google Analytics for that matter) with the unique visitor numbers that Google is now publishing through Google Trends and Ad Planner. I think they will be astonished at how much lower Google now says their traffic is.

I asked Gian to elaborate, and published the resulting interview here.

But until now, we've not had the data to back Gian's claim. I asked him if he could provide it, and to his credit, he did. The story it tells is certainly not what one might expect. (Of course, the data is from Comscore, so it must be taken as such, but remember, Comscore is a public company that stakes its reputation and its market value on data, so my gut tells me that Gian is not trying to pull the wool over anyone's eyes.)

A bit of background: Anyone paying attention has noticed that publishers, by and large, believe Comscore's panel-based measurement system grossly underestimates traffic and unique visitors. As a publisher myself (FM represents more than 160 middle to large sized sites, including this one), I've been one of the most visible such complainants. And that list is not short. In fact, Comscore and Nielsen are both working with the Interactive Advertising Bureau (I am a board member) on anaudit of their practices to verify their methodologies. (Comscore notes that it believes the issue of cookie deletion can cause significant inflation in unique visitors, for more see this release.)

Given this, the world expected that Google, with its unparalleled access to web-wide data, would validate publishers' concerns and show that Comscore's numbers were significantly under-reporting reality.

Turns out, the reverse is true. Gian provided me data comparing Google Ad Planner and ComScore data in two cases. First, for a large sample of 20,163 sites, his shop compared reporting on monthly uniques between the two services. Secondly, Gian pulled out 5,398 sites that are part of the Google Adsense ad network, and ran the same comparison.

The results are pasted in these two charts (provided to me by Comscore):

cs

What to make of the numbers? First off, it's quite interesting to see that Comscore measures, on average, a significantly higher number of uniques across all types of sites. Comscore's numbers are three to three and a half times higher, according to Comscore...

Ed: 

• Comscore adjusts user counts for those who turn-off or delete cookies. Thus, they have been accused of understating unique user counts.
• Google Analytics fails to report 20% or higher of the visitors to a site. This is a bug.