The source for those sorts of detailed analyses of the electorate is Edison Research. The Somerville, New Jersey-based firm has conducted exit polls for the National Election Pool (a consortium of ABC, CBS, NBC, CNN, Fox and The Associated Press) since 2003 — originally in conjunction with Mitofsky International, and since 2006 on its own. But just how does Edison do it?

Joe Lenski, Edison’s co-founder and executive vice president, said the firm will interview voters as they leave the polls at nearly 1,000 locations (a random stratified probability sample of the more than 110,000 physical polling places across the country). And since Edison expects between 35% and 40% of the vote to be cast before Election Day, it also is conducting a phone survey of early and absentee/mail voters, a process that began earlier this week.  ‘

The exit poll is more a set of interlocking surveys than a single, uniform poll. Aside from the phone and in-person components, Edison will field state-specific questionnaires at 350 of its 1,000 or so polling locations, in addition to the national questionnaire all respondents receive. The idea, Lenski said, is to be able to ask about issues that might be particularly relevant in key states.

“In Utah, for example, which has a large Mormon population, we’ll have questions specific to that population,” he said. “And you’ll see bigger state sample sizes in the big battleground states like Florida and Ohio.”

Rather than conducting oral interviews at polling places, Edison gives respondents written questionnaires to fill out. There are a couple of reasons for that, according to Lenski.