Nielsen//NetRatings Weds Panel, Site Data

NEW YORK Nielsen//NetRatings said it would begin combining its panel-based audience data with site-side visitor information.

The move is part of an effort by Nielsen//NetRatings, which is partially owned by Adweek parent VNU, to address discrepancies between the audience numbers it computes through panel data and those recorded by Web sites’ log files.

Web publishers have long complained that Nielsen//NetRatings’ panel data undercounts visitors to their sites, since it does not include publicly used computers and suffers from sampling imperfections.

Nielsen//NetRatings is attempting to address those issues by combining its NetView panel with server data collected by its SiteCensus Web analytics service to create what the measurement firm is calling an “integrated audience” metric that better gauges the actual number of visitors to sites.

Nielsen//NetRatings said it has tested the method in Italy for the past three months. It found that panel data alone tended to undercount site audiences by about 15 percent, said Manish Bhatia, senior vice president of product development and measurement science at Nielsen//NetRatings.

Yet server numbers alone are also skewed, Bhatia said, in large part because of deleted cookies. In the Italian test, Nielsen//NetRatings found that cookie deletion can affect Web sites’ audience reports by as much as 46 percent for search engines and portals, and 23 percent for news and information sites. This results in Web sites erroneously recognizing many return visitors as first-time users.

“It is the reach and frequency where the problem is,” Bhatia said. “Because of cookie deletion, if you look at a report, it is probably overcounting your reach and understating the frequency.”