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Thursday, September 13, 2007

Google Analytics Was Partly Showing Wrong Absolute Visitors

Google’s web statistics service, Analytics, was partly showing the wrong value for “Absolute Unique Visitors,” Google said in a statement. This bug is fixed now, Google says, and was only restricted to the Absolute Unique Visitors details report page, and not the value as taken from the Visitors overview page. But when you visited the former, Google previously made the error of adding up the daily unique visitors; the sum of those days, however, are not the Absolute Unique Visitors value anymore (because the sum includes repeat visitors). A sample calculation I made for one of my sites showed the wrong value to be off by a factor of around 1.6 – the old Analytics would have shown around 95,000 non-existing visitors on the Absolute Unique Visitors details page for the last month!

This case goes to illustrate that even Google gets math wrong sometimes, but the confusion among search statistic providers and those who read the stats don’t stop with this bug-fix, unfortunately. It’s helpful to clarify some terminology:

Now which value you should look at or hand out depends on what you want to measure; “success,” branding, ad views? Or the chance a given person clicks on an ad? Or the chance your server goes down due to traffic? Or something else entirely?

Visits in Google Analytics are one of the best all-purpose measurements, and then you can also look at average time spent on the site (for instance, an important value to a video site which may show commercials alongside the video in specific intervals), and page views. The Absolute Unique Visitor number on the other hand won’t tell you anything about the visitor loyalty; to this number, 10,000 people visiting on Monday only is the same as 10,000 loyal people visiting every day from Monday to Friday. That number is also particularly incomparable to some other stats packages, and it certainly won’t tell you about server traffic. It’s an interesting value, but handle with care and know that you can never sum up the individual time frames for this to get the overall absolute unique visitors number (the error Google themselves made).

In any case, when you compare values from different statistics providers, make sure you compare the same thing – and if you’re asked about your statistics, also make sure the person who asks doesn’t compare your numbers with numbers from other statistics packages, unless you can be precisely sure the two stats “mean” the same thing... especially when it comes to the terms “visit” and “visitor.” And as above news of Google’s bugfix shows, sometimes you even need to ensure you’re also not comparing numbers from a recent version of the statistics software with an older version of it.

*1and1 shows me a German web statistics interface. They use the term “Besucher,” which translates to “visitor.” (“visit” on the other hand would translate to “Besuch”).


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