Advocacy groups of all stripes, it seems, are increasingly using opportune moments to chime in on Twitter to get their points across, and so a new year-long study on just how comparable Twitter users are in their reactions to political events to the general public seems like a worthwhile opportunity to re-examine just what role the tool should be playing in our national political conversation.

The Pew Research Center study confirmed what everyone suspected: People who use Twitter to share their opinions don't reflect the general public's opinion as a whole.

"The lack of consistent correspondence between Twitter reaction and public opinion is partly a reflection of the fact that those who get news on Twitter -- and particularly those who tweet news -- are very different demographically from the public," Pew reported on Monday. "Twitter users are not representative of the public."

Pew's surveys find that Twitter users are younger than the general public and more likely to be Democrats or lean toward the Democratic Party. Many users are abroad, as techPresident Editorial Director Micah Sifry pointed out in his piece last year about the Twitter Political Index and voter sentiment. And many who participate in the conversation on Twitter can't do so in public opinion surveys because they are not 18 years old. Pew's 2012 biennial news consumption survey also found that only 13 percent of adults said they ever use the micro-blogging service.

Moreover, the people who choose to voice their opinions on Twitter are self-selecting, Pew notes.

"Perhaps most important, the Twitter users who choose to share their views on events vary with the topics in the news," Pew reports. "Those who tweeted about the California same-sex marriage ruling were likely not the same group as those who tweeted about Obama's inaugural or [Mitt] Romney's selection of [Paul] Ryan."

Pew tracked eight different events throughout 2012 to arrive at its conclusions. It found, for example, that when a court found the California ban on same-sex marriage unconstitutional, in a quantitative sense the reaction on Twitter tended to be more positive (46 percent) than negative (eight percent).

But a public opinion poll at the same time found that of those who had heard about the ruling, just 33 percent were happy, or very happy with the news, compared with 44 percent who were "disappointed or angry." The survey found similar disparities on reactions to presidential candidate debate performance, and to Obama's re-election.

Pew's new survey also notes that it was the negativity on Twitter during the 2012 election cycle that stood out.

"For both candidates, negative comments exceeded positive comments by a wide margin throughout the fall campaign season. But from September through November, Romney was consistently the target of more negative reactions than was Obama," it reports.

All this is worth noting simply because news anchors and reporters use Twitter as a tool to try and check citizens' reactions to news events in real-time. As Will Oremus notes on Slate, it's our version of trying to get an opinion from the man on the street. Moreover, political campaigns across the board during the 2012 cycle spent many resources to monitor and use Twitter in an effective way.

Josh Koster, managing partner at the Democratic digital advertising firm Chong + Koster in Washington, DC, downplayed the findings of the survey.

From an advertising viewpoint, "I would say it's not a big deal," Koster said. That's because groups often will use Twitter to reach out to the media, whose denizens use Twitter obsessively.

"Pretty much all reporters use Twitter, and Twitter ads are run for press visibility as much as for voter visibility," he said in a phone conversation.