The consolidation of companies that measure Internet usage continued on Tuesday when Neilsen Media Research bought a piece of Silicon Valley start-up Net Ratings.

The new deal comes just two weeks after their competitors, Media Metrix and Relevant Knowledge, announced they would merge.

Neilsen Media Research, which is best known for its TV audience tracking, brings to the new alliance what it says is a panel of users that will be representative of the Internet population. Net Ratings brings its measurement software, which tracks Web site activity.

The new service, which will debut early next year, will offer to track advertising exposures, provide projectable demographic information, and determine the effectiveness of advertising in reaching various demographic groups.

The financial terms of the agreement were not revealed but the companies but they said Neilson would acquire a "significant" equity position in its new partner.

John Dimling, chief executive of Neilson Media Research, said the announcement "moves the entire industry closer to the day when strategies for using the Internet can be based on accurate, reliable and consistent information".

Industry watchers believe that Neilsen had to speed up its entry into the Web monitoring business so that it is a major player when the convergence of television and digital media actually happens.

Back on 12 October Media Metrix and Relevant Knowledge said they would merge into a company called Media Matrix. The aims of that combination are to provide reporting on a representative sample of more than 40,000 users and 15,000 Web sites.

The Web ratings arena has long been mired in controversy with the four participants, plus a fifth - PC Data - giving wildly different figures for an audit of the same site.

Media Matrix has tried to counter that by saying that its audits and those of Relevant Knowledge were actually close, once you matched the underlying definitions, such as the minimum age of users.

Analysts are saying there is room for the two combinations, especially as they currently track different universes. Neilsen/Net Ratings has strength with the home based Internet surfer, while Media Matrix tries to audit users who log in at work.