NEW YORK: TV networks and advertisers are to change how they measure audiences for advertising purposes in order to take account of changing viewer habits.

The Wall Street Journal reported that major US networks, including NBC, ABC, Fox and CBS, had struck deals with media buying agency GroupM that would mean viewing figures would be included for the seven days after a prime-time show first airs rather than the current three days.

Figures from TiVo, based on the 2012-13 season, indicated that such a move could result in an uplift of between 4% and 11% in audience numbers for the most popular programmes.

During Fox's recent upfront, ad sales chief Toby Byrne had signalled the need to discuss this issue. "With so much of our audience choosing to watch on their own schedule, our business needs to evolve as well," he said.

With higher ratings, networks would ultimately be able to demand higher payments, but at first they may have to actually cut rates in order to encourage buyers to make the switch from a three-day measurement period to a seven-day one.

Rino Scanzoni, chief investment officer at GroupM, made the point to the Wall Street Journal last month: "It's a matter of working out the economics initially to make the transition one that's acceptable to both sides."

The paper noted, however, that many marketers would be reluctant to change as they currently had the upper hand in a buyer's market, with networks battling falling ratings. Further, if viewers were already watching their ads after three days there was no incentive to move to seven days and pay for what is now 'free'.

Audience measurement has become an increasingly complex business as the universe of devices and platforms expands. Measurement organisations such as the British Audience Research Bureau already have to deal with traditional survey data as well as device-based data from webservers and set-top boxes.

And while these can take account of people viewing programmes after broadcast, BARB told Warc's MAP conference it is also looking to develop a measure for programmes shown online before broadcast.

Data sourced from Wall Street Journal; additional content by Warc staff