All right, let's go back a few weeks to Election Day 2012 and take a look at exit polls.
According to the New York Times, the Election Day polls were based on questionnaires completed by voters when they left voting stations around the country on Tuesday, November 16th. These questionnaires were supplemented by telephone interviews with absentee and early voters. The polls were conducted by a variety of different entities, including Edison Research of Somerville, N.J., for the National Election Pool, a consortium of ABC News, Associated Press, CBS News, CNN, Fox News and NBC News.
The national results were based on voters in 350 randomly chosen precincts across the United States, and included absentee voters and early voters who were interviewed by telephone. The state results, however, were based on voters in 11 to 50 randomly selected precincts across each of 18 states analyzed by The Times. In some states, a portion of the interviews were also conducted by telephone with absentee voters and early voters.
Results that were based on smaller subgroups of individuals, such as demographic groupings, have a greater potential sampling error. In addition to sampling error, the genreal difficulties of conducting any survey of voter opinion on Election Day, such as the reluctance of some individuals to take the actual time to fill out the questionnaire, may have introduced other sources of error into these polls.
I didn't know sampling error played such a large role in Election Day exit polls. I'll have to keep this in mind next time Election Day rolls around...
Check out the 2012 Election Day Exit Polls at the New York Times.