Twitter now posts a "daily sentiment" index about the candidates. Watch what you say... literally.

National Journal:

Negative conversations about the presumptive GOP nominee spiked at the end of last week, after Romney’s criticism of Britain’s handling of security at the Summer Olympics in London. The survey, which tracks word-of-mouth discussions among adults, found that on Sunday, 49 percent of conversations about Romney were negative, a 7 percentage-point spike from the previous day’s tracking. The survey works on a three-day rolling average. Over the course of last week, 45 percent of word-of-mouth discussions about Romney were mostly negative while only 27 percent were positive. Discussions about President Obama, meanwhile, were split evenly at 40 percent.

Plugging decades of data into spreadsheets, they calculate everything from how much a bad economy is hurting an incumbent to how the results of New Hampshire's presidential primaries, conducted 10 months before an election, can signal who the eventual winner will be in November.

"What this forecasting really amounts to is quantitative history," said James Campbell, a political scientist at the University at Buffalo, SUNY.

So far this year, forecasters in line with many current opinion polls see Obama squeaking out a victory over Romney.

In a Reuters poll of nine leading forecasters, the median prediction was for Obama to win 50.5 percent of the vote. Although under the complicated American system, that would not necessarily mean victory because the winner is determined by the state Electoral College results.

In 2008, the median forecast of the same group, which estimated that Obama would receive 52 percent of the vote compared with Republican John McCain's 48 percent, was about as close to the election results as Gallup's final poll from the last three days of the presidential campaign.