Exit poll and related survey methodology -- 2012 general election

Key facts and methodology details about voter surveys in the Nov. 6, 2012, general elections:

• Conducted for The Associated Press and other members of the National Election Pool (ABC, CBS, CNN, FOX and NBC) by Edison Research
• Coverage: Surveys of voters nationally and in 31 states in the 2012 presidential and other statewide elections
• How many interviewed: About 60,000 voters nationwide for survey analysis, tens of thousands more in larger sample for projections purposes.
• most reached in traditional "exit polls" (a technique first used four decades ago) as they exit the voting booth
• including nearly 10,500 early voters reached from Oct. 29 through Nov. 4 in "random digit dial" surveys of households with landline or cellular telephones
• Exit polls: Stratified probability sample, taking into account population size and past voting history, of nearly 1,000 voting precincts nationwide -- from 10 to 50 per state where statewide exit polling was conducted.
• At each sampling location an interviewer approaches voters at a specified interval -- for example, every fifth voter -- as he or she exits the polling place. The interval helps ensure the randomness of the sample. The sample is designed so that everyone who votes in the general election has a known probability of being included.
• Participation is voluntary and anonymous.
• The National Election Pool prepared the questionnaire, including questions about demographics such as gender, age, race, and issues related to the person's vote choice.
• The interviewing starts when the polls open and continue throughout the day until about an hour before polls close.
• Telephone polls
• In 14 states with high rates of early or absentee voting or where nearly all voting is done by mail, NEP commissioned telephone surveys to reach pre-Election Day voters.
• In 11 of those states -- Arizona, California, Florida, Iowa, Michigan, Montana, Nevada, New Mexico, North Carolina, Ohio and Wisconsin -- the phone data were blended with exit poll results, with the phone poll results weighted to represent the expected share of early vote in the electorate.
• There are phone polls only, with no exit polls, in Colorado (with nearly eight in 10 voting early in 2008) and Oregon and Washington (where all or nearly all voting is done by mail).

· Sampling error: All samples are approximations. A measure of the approximation is called the sampling error. Sampling error is affected by the design of the sample, the characteristic being measured and the number of people who have the characteristic. If a characteristic is found in roughly the same proportions in all precincts ("non-clustered") the sampling error will be lower. If the characteristic is concentrated in a few precincts the sampling error will be larger. Gender would be a good example of a characteristic with a lower sampling error. Characteristics for minority racial groups will have larger sampling errors.

The table below lists typical sampling errors for this exit poll for non-clustered characteristics at the 95 percent confidence interval. No more than one time in 20 should chance variations in the sample cause the results to vary by more than this amount for non-clustered characteristics. However, non-sampling factors such as question wording and order and voter non-response may increase total error.

Respondents	Margin of sampling error
100	plus or minus 15 percentage points
101 - 200	plus or minus 10 percentage points
201 - 500	plus or minus 7 percentage points
501 - 950	plus or minus 5 percentage points
951 - 2350	plus or minus 4 percentage points
2351 - 5250	plus or minus 3 percentage points
5251+	plus or minus 2 percentage points