Not so online. In May, comScore gave Yahoo 34 million more unique visitors (167 million) than Nielsen did (133 million). But it probably won’t cost Yahoo a penny if everyone believes the lower number, because Yahoo isn’t selling its total reach. Instead, Yahoo and other sites sell “ad impressions,” or sometimes actual “clicks,” which tally up one by one. Every time a banner loads up in front of you, the advertiser owes a little more money.

Advertisers and agencies still use third-party ratings to plan their campaigns. And sites with demographically appealing audiences, like the Times and the Journal, will flaunt those statistics to entice marketing departments. But this sort of planning is less decisive since advertisers can watch their campaigns play out live and make adjustments on the fly, based on which Web sites send more customers their way.

This is not to say that accuracy is passé. Some number of people was drawn to The Miami Herald’s Haiti coverage, and it would be helpful to know what that number is. “There are a lot of optional, high-cost, high-effort editorial projects a newspaper can choose to pursue,” says Rick Hirsch. “I wish I had the data to guide these editorial choices. Ironically, it’s still like being a traditional editor, making calls based on your gut instinct—you have more data, but it’s conflicting.”

One way through the morass is for publishers to learn to ignore the numbers they don’t trust. It seems inevitable that, over time, this will mean more emphasis on mining their own server stats. For the last year, the Times, Gawker, TPM, and other outlets have been testing a site-analysis tool called ChartBeat that focuses on the last fifteen seconds of activity at their sites: what people are reading, commenting on, searching for, linking to, and Twittering about. One startling revelation at TPM: almost all of the audience drops off before the halfway point of longer pieces. Such real-time diagnostics raises thorny journalistic questions, but it also makes monthly site rankings seem irrelevant.

And what about the clarity the industry yearns for? The only way to imbue an audience number with anything like the authority of the old TV ratings is with a new monopoly—if either Nielsen or comScore folds or, more likely, they merge. That kind of authority won’t mean greater accuracy, just less argument. Advertisers don’t need it, and Web sites shouldn’t want it.

This article was adapted from “Chaos Online: How a Faulty Metrics Affect Digital Journalism,” a report written by Graves, John Kelly, and Marissa Gluck. It was commissioned by Columbia’s Graduate School of Journalism and funding for the research was provided by Mary Graham, a member of the school’s Board of Visitors. The full report is available at www.journalism.columbia.edu/onlinedata.

Lucas Graves is an assistant professor in the school of journalism and mass communication at the University of Wisconsin. Follow him on Twitter at @gravesmatter.