America's two online audience measurement services are under fire over the accuracy of their data.

Several internet publishers and media buyers are calling on ComScore Media Metrix and Nielsen/NetRatings to improve their methodologies. The most common complaints are about the research firms' panels and the way they study the prized at-work audiences.

"The bottom line is the numbers are not right," grumbled David Cohen, senior vp and interactive media director at Universal McCann Interactive. "They're wrong, and decisions are being made on billions of dollars in ad spending against these numbers, which are erroneous."

Cohen believes that figures from both measuring firms can be anything from 80% to 130% off in terms of reach and frequency. His comments chime with findings from, where -- according to vp of marketing Bruce Rogers -- ComScore's traffic figures are 50% to 100% lower than those given by Forbes' internal log files.

America Online is also unhappy. Howard Schimmel, vp of market research, complained: "We don't have enough insight or information to make smart programming decisions."

Schimmel is keen for online ratings to match TV measurement, with in-depth day-part information and next-day figures.

Nielsen has a panel of 43,600, of which 5,950 are classed as 'at-work'. They are recruited by random phone calls. ComScore uses 100,000, with 50,000 at-home, 30,000 at-work and 20,000 in universities. To enrol participants, it uses random calling and banner ads offering extra web services in return.

Each firm defended its methods and attacked its rival. ComScore claims Nielsen's at-work panel is too small; Nielsen argues a larger panel does not necessarily mean greater accuracy.

Nevertheless, ComScore is in talks about its methodology with trade organisations such as the Media Ratings Council, the Internet Advertising Bureau and the Online Publishers Association.

"We certainly believe there's a role for the industry bodies to play here," declared division president Peter Daboll. "But it's a much more complex process in the internet space than in the TV world."

Data sourced from:; additional content by WARC staff