The rough version of how it works: Topsy pores through every single tweet in real time, determines which ones are about Obama or Romney, and then assigns a sentiment score to each tweet based on its content. That is, whether it’s positive or negative toward Obama or Romney, and just how positive or negative it is. Add all the data up together and you have something like a real-time approval score for Obama and Romney, determined by what tens of millions of people are saying, which Twitter is going to release daily at election.twitter.com.
Again, it’s scale of the data that makes this project so powerful. With Topsy’s access to the full Twitter firehose, it’s processing 400 million tweets a day in real-time. To compare, on Election Day 2008, there were 1.8 million tweets. There are that many tweets every six minutes today.