The Interactive Advertising Bureau is pressuring the industry's major third-party metrics firms to improve the accuracy of the traffic data they report, in response to an increasing number of complaints from web publishers.

Major websites such as MSNBC.com claim that the traffic data it collects varies by as much as 30 percent from the data reported by metric firms, according to AdWeek. Several top publishers are reporting that the gap is widening between the traffic data collected internally and the same data as reported by Nielsen//NetRatings and comScore Media Metrix. These complaints are intensifying just as both firms prepare to undergo long-awaited Media Rating Council-led audits.

Accurate traffic tracking is vital to media buyers, especially those looking to establish campaign reach or who are buying outside of a normal CPM deal. Moving forward, some favor a combination of third-party and self-reporting from sites, with which Nielsen is already experimenting.