Can you scientifically quantify social media opinion?

Over at NBCNews.com, we’ve started publishing daily charts tracking what people are saying about the presidential and vice presidential candidates on Twitter and Facebook. Here’s today’s for the weekend (click here for the full-size version):

In my analysis, I write:

In recent weeks, Obama has generally led Romney by two to seven percentage points in national polls, which carefully select their samples to reflect Americans most engaged in the election and registered to vote.

The picture is different among Americans who have gone online to talk about the election, however — NBCPolitics.com’s analysis indicates that that narrower but more diverse sample of the country prefers Romney by 36 percent to 32 percent overall and by 51 percent to 49 percent when they’re compared head to head: