Image credit: Twitter

Want to see who is ahead in the presidential race based on tweets and only tweets?

Today Twitter launched its Political Index, a dedicated site at http://election.twitter.com, which will show whether President Obama or Republican candidate Mitt Romney is in the lead based on millions of 140-character messages.

"We started by looking at the explosion at tweet volume since last election. There were 1.8 million tweets on the election day in 2008. That's about six minutes on Twitter today, "Adam Sharp, Twitter's head of government news and social innovation, told ABC News. "We were looking at follower growth and audience reaction to the State of Union and what we discovered was that the conversation, which were happening in a measurable public space, could be used to create a real-time index."

The Twitter Political Index or TwIndex, as Twitter calls it, is an attempt to quantify all those tweets and data. The company has teamed up with a social media analytics firm named Topsy to analyze tweets with different words related to the campaign. Topsy looks at a number of things in a tweet - words, phrases, combinations of words, etc. - when assigning a positive or negative rating. Like an approval rating, the index scale runs from zero to 100. Topsy and Twitter are also working with two polling firms - Mellman Group and North Star Opinion Research.

ABC News has employed a similar system on its OTUS News site with the help of Bluefin Labs, which analyzes social sentiment from publicly available Facebook & Twitter comments, search, trending, and influencer data. Similarly, the London Eye ferris wheel currently changes the color of its lights based on London's Twitter sentiment surrounding the 2012 Olympics.

The http://election.twitter.com site is live and showed President Obama having a higher rating than Romney, though it is down by -4 since yesterday.