From autumn 2013, the exclusive multi-year agreement will create the "Nielsen Twitter TV Rating", designed to be a syndicated-standard metric around the reach of the TV conversation on Twitter, including online and mobile conversations.
Increasingly advertisers are looking to measure both the "paid" and "earned" media impact of their integrated campaigns, and this new metric aims to track comments about TV programmes and ads generated on second screens of tablets or smartphones.
Viewers discussing TV content on social media, and particularly the real-time feeds of Twitter, have created a new dynamic between audiences and programming. Many programmes and some ad campaigns already seek to generate and harness reactions on Twitter, but there has been no standard way to measure such activity.
Steve Hasker, president of global media products and advertiser solutions at Nielsen, called the Nielsen Twitter TV Rating, "a significant step forward for the industry".
Highlighting how programmers are developing increasingly captivating live TV and new second-screen experiences, Hasker added: "As a media measurement leader we recognise that Twitter is the pre-eminent source of real-time television engagement data."
The Nielsen Twitter TV Rating will serve to complement Nielsen’s existing TV ratings, giving TV networks and advertisers the real-time metrics required to understand TV audience social activity.
There is no indication if and when the service will be rolled out in the UK, but it is widely believed the market will be among the first to trial the new metric once established in the US.
There has been a cautious initial reaction to the news. Tess Alps, executive chair of commercial TV marketing body Thinkbox, warned that viewer sentiment could be lost if a numerically based system takes hold.
Alps also railed against use of the contentious and ill-defined concept of "engagement", and noted that the biggest programmes on television do not necessarily equate to the most amount of tweets, although many of them do.
"Sometimes the more absorbed you are in a programme, the less viewers are likely to tweet," said Alps. "For example, with quality drama like Game of Thrones, there are not many viewers tweeting. ITV’s popular X Factor meanwhile always receives high volumes as it is a participatory live programme, as do major live sporting events."
Twitter UK’s commercial director, Bruce Daisley, acknowledged there are "very different patterns for drama" but stressed that the new metric will "help brands identify big second screen shows".
Earlier this year, The Screen Life study from Thinkbox and COG Research, blended analysis of video footage of 23 households' living rooms with an online survey of 2,000 people. It suggested that 86% people with access to TV and the internet have "multi-screened", while 34% say they do so regularly. It also found that 31% have chatted about TV shows or ads in a second screen, but that this rose to 56% for 16-24 year-olds.
Chloe Sladden, vice president of media at Twitter, said: "Our users love the shared experience of watching television while engaging with other viewers and show talent. Twitter has become the world's digital water cooler, where conversations about TV happen in real time. Nielsen is who the networks rely on to give better content to viewers and clearer results to marketers."
David Poltrack, chief research officer at US broadcaster CBS Corporation, said he was "pleased" to see Nielsen and Twitter join together. He added: "The proliferation of smartphones and tablets has generated a substantial ‘connected’ TV audience that is simultaneously watching television and accessing the Internet through these devices.
"This, in turn, will continue to create the opportunity for content providers like CBS to offer engaging interactive features for our viewers. As this form of viewer engagement evolves into a mainstream activity, it presents ways for CBS to enhance the viewing experience for our viewers and our advertisers.
"We are already engaged with Nielsen and Twitter in a programme of research and experimentation in this exciting new area."