Twitter is a great way to get a glimpse of what people are talking about. But the social media site falls short of being a reliable barometer for public opinion, a new Pew Research Center study revealed.

Reactions and conversations on Twitter often differ sharply from the results of public opinion polls, particularly when it comes to political events and policy decisions, the study concluded. Often the tone of Twitter exchanges leans more liberal than national surveys of public opinion. But the inverse can happen as well, based on the topic at hand and who decides to participate in the conversation.

When a federal court ruled that a California law banning same-sex marriage was unconstitutional last February, Twitter conversations about the ruling were much more positive (46 percent) than negative (8 percent). But public opinion, as measured in a national poll, went the other way: just 33 percent of respondents were happy about the ruling, while 44 percent expressed a negative opinion. The reaction to President Obama’s 2013 inauguration speech, on the other hand, reflected the inverse. Public opinion polls gleaned a 48 percent positive response and 22 percent negative, while on Twitter only 13 percent of posts were positive, 21 percent negative, and a whopping 65 percent a ho-hum neutral.  

Demographics, the Pew Research Center said, may account for much of the disconnect. Twitter users tend to be younger than the overall, general public.

In another recent Pew survey, half the adults who said they posted news on Twitter were younger than 30. The Twittersphere also veers toward the left in the U.S., with 57 percent of those posting saying they were Democrats or leaned Democrat, compared with 46 percent of the general public.

Twitter also has a relatively modest reach, as evidenced by a previous study: only 13 percent of adults use Twitter or read Twitter messages, and a mere 3 percent said they regularly or sometimes tweet or retweet news. One in five American adults don’t even use the internet.

But in another sense, the Twitter conversation can be broader and more diverse than surveys of public opinion. National surveys are limited to adults who are 18 years of age and older, while voices of any age can hop into a Twitter discussion. National surveys are also restricted to U.S. residents, while Twitter is accessible to anyone anywhere.