A second look at the ‘second screen’

October 8, 2013, 2:25 PM UTC

FORTUNE — Social-media enthusiasts, especially those on Twitter, tend to think their hobby is more popular than it really is. If you’re on Twitter a lot, and the people you know best are on Twitter a lot, it’s easy to delude yourself into thinking that the whole world is there with you. But it’s not. Most people work or go to school all day, and when they get home, many of them just want to flop down on the couch in front of the TV (or maybe read a book, or do some knitting, or chat face-to-face or on the phone with friends and family). The last thing on their minds is logging into Twitter to yammer.

And that includes yammering about their favorite TV shows. The Wall Street Journal has compared the “Twitter ratings” compiled by Nielsen through its new SocialGuide service to TV ratings, and noted a big disconnect between some of TV’s most popular shows and so-called second-screen viewing — which in this case means people tweeting about the shows they’re watching. The most-tweeted shows, it turns out, generally aren’t among the most popular.

Networks, advertisers, and social-media services including Twitter and Facebook (FB) are trying to capitalize on the “second screen” phenomenon,” but it appears that, even if they are successful, the rewards will be marginal at best.

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The data, the Journal concludes, serve as “a reminder that the social-media service’s user base has a very different makeup than the mass-market TV-viewing audience that marketers spend tens of billions of dollars each year to reach.”

Twitter, after all, has only about 49 million users in the U.S., and only a fraction of them tweet regularly about TV.

Which is not to say it’s pointless to try to understand and reach those users. But it’s difficult to understand one marketer’s conclusions about the value of second-screening: If people are tweeting about TV shows, that “means the ads are also being paid attention to,” Steve Kalb, director of video investment at the ad firm Mullen, told the Journal. But doesn’t it more likely mean that Twitter is being paid attention to?

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Twitter, which is getting ready to go public, thinks it can be both — if the ads are on Twitter itself. It has explicitly stated that it’s seeking TV-related ads, including through its Amplify program, which presents video clips with ads for shows embedded in the tweet stream.

Twitter certainly has the power of buzz behind it: If your friends are tweeting about a show, you’re more likely to check it out for yourself. After that, though, the show has to stand on its own.

As noted in a report last week, from eMarketer, sports and other live-viewing events like The Voice and American Idol, naturally lend themselves to second-screen viewing. That’s where most of the opportunities probably lie. Furthermore, Twitter skews young and urban, so the perfect target for these efforts might be a 22-year-old baseball fan who watches a lot of reality TV.

Trying to reach the couch-floppers who prefer mass-market sitcoms and dramas, though, might be largely a wasted effort.