Today Nielsen, the venerable measurement service, shed light on the question of how online social media “buzz” relates to TV ratings. In a study done jointly with the McKinsey consultancy, the company found that within a few weeks prior to the premiere of a new television show, a 9 percent increase in social media comments correlates to a 1 percent increase in ratings among people aged 18 to 34, who are the most active social networkers. Later in the TV season, it takes a 14 percent increase in buzz to correspond to a one percent increase in ratings. This correlation is statistically significant, and the analysis is the first to make such a link, according to Radha Subramanyam, Nielsen’s senior vice president of media analytics and Nielsen and NM Incite, the joint venture between Nielsen and McKinsey.

Subramanyam doesn’t claim that the buzz actually causes the ratings boost. But it does suggest something else important: research on social media activity is on its way to producing a reliable metric for real-world trends and behaviors. I’ll go out on a limb and say that what Nielsen did was show that, eventually, it might become possible for the right measurement and analysis of social-media comments to serve as a proxy for today’s widely-accepted measures on all sorts of things, including TV viewership, sales, and even voting behavior.

The caveats are several, of course. In the television context, for example, men over 50 aren’t very likely to tweet about Andy Rooney’s retirement and the future of 60 Minutes. (You’re more likely to get good data on Glee or Jersey Shore.) But the trend is toward more, not less, social media engagement. And two-screen behavior—in which people use laptops or smart phones while also watching TV—is on the rise. As Subramanyam points out: “As television becomes more digital—in the form of sharable video clips or articles about a show’s premiere, for example—social media will continue to play an increasingly important role in how consumers discover and engage with various forms of content, including TV.”

The causation question came up when I was reporting our upcoming feature, posting October 18, on Bluefin Labs, a startup company in Cambridge, Massachusetts, that is trying to precisely pin social media comments to the TV shows and advertisements that provoke them. (The company leaves it to others, such as Nielsen, to measure viewership.) “We’d love to know the connection between social media and ratings,” Gayle Weiswasser, the vice president of social media communications for Discovery Communications (which owns Discovery Channel and several others), told me. “Is there a causative relationship? Or are they simply correlated?” She will have to wait awhile longer for that answer; Nielsen and others are plugging away. But with more data being generated all the time, and more companies discovering business models in producing analytics, the tools for figuring this out are getting sharper.

Details on the study’s findings and methodology can be found here.