According to Twitter official blog, they launched a new barometer for the election.

The Twitter Political Index is a daily measurement of  Twitter users’ feelings towards the candidates as expressed in nearly two million Tweets each week.
twitter political index
The Twitter Political Index is built in partnership with the data analysis team at Topsy(@Topsy) and two respected polling firms: The Mellman Group (@markmellman) andNorth Star Opinion Research (@northstaropin).Each day, the Index evaluates and weighs the sentiment of Tweets mentioning Obama or Romney relative to the more than 400 million Tweets sent on all other topics. For example, a score of 73 for a candidate indicates that Tweets containing their name or account name are on average more positive than 73 percent of all Tweets.Just as new technologies like radar and satellite joined the thermometer and barometer to give forecasters a more complete picture of the weather, so too can the Index join traditional methods like surveys and focus groups to tell a fuller story of political forecasts. It lends new insight into the feelings of the electorate, but is not intended to replace traditional polling — rather, it reinforces it.For example, the trend in Twitter Political Index scores for President Obama over the last two years often parallel his approval ratings from Gallup, frequently even hinting at where the poll numbers are headed. But what’s more interesting are the periods when these data sets do not align, like when his daily scores following the raid that killed Osama bin Laden dropped off more quickly than his poll numbers, as the Twitter conversation returned to being more focused on economic issues.

By illustrating instances when unprompted, natural conversation deviates from responses to specific survey questions, the Twitter Political Index helps capture the nuances of public opinion.

The Index for each candidate updates every day after 8 p.m. ET to reflect shifts in conversation from that day’s events, and is available along with a historical chart During the runup to the election, our partners will be featuring this data on their sites as well: Topsy will be posting detailed analysis, and USA Today is using the Index to create the USA Today/Twitter election meter throughout the campaign. We’ll also tweet daily updates and other observations at @gov.

Posted by Adam Sharp, Head of Government, News and Social Innovation – @AdamS