Our chapter on public opinion discusses various ways to gauge sentiment. The Pew Research Center reports:
The reaction on Twitter to major political events and policy decisions often differs a great deal from public opinion as measured by surveys. This is the conclusion of a year-long Pew Research Center study that compared the results of national polls to the tone of tweets in response to eight major news events, including the outcome of the presidential election, the first presidential debate and major speeches by Barack Obama.
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. Much of the difference may have to do with both the narrow sliver of the public represented on Twitter as well as who among that slice chose to take part in any one conversation.