My lucky numbers
Publishers like the census method because they know exactly where the data comes from. But panel proponents say that census methods inflate the audience count by including visits by spiders and bots, as well as by counting people who delete their cookies as unique every time they come back.
Manish Bhatia, president of global services & U.S. sales for Nielsen Online, says server logs inflate traffic counts by 20-50 percent, depending on the site.
The network-centric methodology eliminates the cookie deletion issue, according to Marc Johnson, CMO for Hitwise. "We don't rely on cookies or individuals themselves," he says. Instead, the company's ISP partners install its software in their networks, analyze usage logs and feed the anonymous data to Hitwise. (But just to make things more confusing, Hitwise could be placed in the panel camp, because it doesn't measure all internet traffic, just a sample of it, albeit a very large one.)
Most of the cookie- or tag-based services do some number crunching to account for cookie deletion, and insist this isn't a problem.
Critics say that ISP data may show more unique users than there really are due to dynamic IP addressing. Moreover, it may count foreign site visitors as in-country because they come in on domestic IP addresses.
The census school counters that "professional panelists," people who join panels or respond to surveys for the incentives or because they're bored, skew results. In a 2005 presentation at the Marketing Research Association Conference, comScore chairman Gian Fulgoni said that the internet survey population has been over-fished: 0.25 percent of all internet households account for 30 percent of all surveys taken online, and, on average, a member of each of the leading panels belongs to at least eight other panels.
ComScore says it recruits from a wide variety of sites that other online surveyors don't use. It has software to screen out these serial panelists, for example, by counting how many surveys they fill out, and that its 2 million panelists outweigh the few pros.
Nielsen Online guards the purity of its panelists by only doing outbound recruiting. It generates statistically random lists of panelists that are geographically and demographically representative of the population, and then calls them up, inviting them to join.
"If you'd ask, 'How do I get on your panel,' I'd say, 'You can't,'" Bhatia says.
However, Neilson Online's recruiting relies on the telephone, and, because they're not allowed to call mobile phone numbers, scoffers say their panels may not represent the youngest, most tech-savvy citizens who don't have land lines.
And so it goes.