Online advertising is a numbers game -- and that's supposed to be its strength. "Everything is trackable and measurable," the mantra goes.
When it comes to audience measurement, though, not everyone is using the same ruler. That leads to knuckle-whitening discrepancies in which a third-party service may size a publisher's audience at 50 percent less than what its internal numbers show.
What's at stake?
"If you under-represent by 20 or 30 or 40 percent the audience for something, that can have massive implications for media planning and for the perceived value of those properties," Yankee group analyst Daniel Taylor says.
Who's right? That's an argument that may never be solved.
Before we get into the latest salvos in this battle, let's do a quick reprise of the methodologies. There are two basic ways of measuring the number of unique visitors to a website: trying to count each one, the census method, or estimating the number by extrapolating from a carefully selected group, also known as a panel.
The most direct way of taking a census is to use server logs, but it's not the only way. Network-centric services tap into the data provided by ISPs and measure where their traffic goes. Some third-party measurement services rely on dropping cookies to track unique users; others tag each page of a site and then count the tags.
Alternatively, you can gather a bunch of people you believe are representative of the universe of internet users, watch what they do, and extrapolate their behavior to everyone else's. This panel approach follows a statistical model that scientists of all stripes rely on for their research; Arthur Nielsen pioneered its use for measuring television audiences in the 1940s.
No matter which method an audience measurement service starts with, each of them use top-secret formulas to weight the results, measuring them against other databases and known quantities to get what they think are the most accurate results.
It's not surprising that the census, or site-centric method, leads to disputes. After all, after 10 years, we still can't agree on what an online impression is. Neither is it shocking that the panel method is under fire.
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