With so much ad money at stake, it's more important than ever that publishers know how many visitors they get, reports the Los Angeles Times.

While that should be a simple process, the unknown methodologies used by firms to measure audience figures lead to vast disparities in reporting data. Moves by firms like comScore and Nielsen NetRatings to bring light (in the form of MRC accreditation) to their work underscore just how important solid figures are.

Right now publishers in some cases report their own, unaccredited numbers, numbers that experts advise not to use when buying ads. The use of panels of people, who then report verbally on their online behavior, is also coming under scrutiny but is still accepted as a basis for buying.

Top online measurement firms utilize a mixture of automated visitor tracking and panel reporting to compile their numbers, a process the MRC and others will be examining as the issue moves forward.