If you’re on Twitter, you know that users there have some pretty strong opinions on what’s currently going on in the world. But a new study from Pew calls into question the reliability of Twitter as a true gauge for public sentiment.

In the study, Pew looked at eight different major news events over the past year. They compared each event in terms of positive and negative opinions – on one side stemming from public opinion polls and on the other side Twitter reaction. What they found was that most of the time, the sentiment expressed by Twitter users didn’t align with the sentiment expressed by Americans in national polls.

Take for instance the times in which Twitter reaction was much more “liberal” than public opinion polls showed. When President Obama was reelected, 52% of those asked in public opinion polls were “happy” about it, as opposed to 45% that were “unhappy.” But on Twitter, his reelection generated 77% positive feedback.

And in February 2012, when the California gay-marriage ban was deemed unconstitutional, only 8% of Twitter users had a negative reaction to it. Public opinion polls showed that 44% did.

Twitter doesn’t always lean more liberal, however. Take for instance Obama’s recent inaugural speech. Although 48% of the public opinion poll respondents reacted positively toward it, only 13% of Twitter users did.

In only two of the eight cases studied did public opinion match well with Twitter sentiment.

But in general, Twitter users tend to lean more Democratic and younger.

Twitter users are not representative of the public. Most notably, Twitter users are considerably younger than the general public and more likely to be Democrats or lean toward the Democratic Party. In the 2012 news consumption survey, half (50%) of adults who said they posted news on Twitter were younger than 30, compared with 23% of all adults. And 57% of those who posted news on Twitter were either Democrats or leaned Democratic, compared with 46% of the general public.

One final thought from Pew:

“At times the Twitter conversation is more liberal than survey responses, while at other times it is more conservative. Often it is the overall negativity that stands out.”

So we can’t always count on Twitter to accurately depict the views of all Americans. But one thing we can count on is that, more often than not, Twitter users are going to give you the cynical side of things.