Sample Precinct

Sample precinct refers to a sampling unit used in data collection and analysis on Election Day. The term is most commonly associated with media exit polling and election night projections. For voting purposes, jurisdictions such as counties or townships are divided into precincts based on geography. A precinct is the smallest voting unit in a jurisdiction. Voters are assigned to a precinct, which typically has one polling place where voters can go to cast their ballots. Data are collected from sample precincts, which are used to form estimates of the vote and voter opinions and characteristics.

For Election Day analysis, a sample of precincts is selected because it would be too costly and time consuming to collect data from all precincts in a jurisdiction (e.g. a state or city). Prior to the election, a representative sample of precincts is selected for a given jurisdiction. A listing of all precincts in the jurisdiction is compiled, and a probability sample of precincts is selected. Typically, stratified sampling is used to increase the precision of the estimates. Precincts can be stratified using such variables as historical voting patterns, geography, and race/ethnicity.

In practice, sample precincts are used for two purposes. The first is to provide data to project the outcome of the election using actual votes from the sample precincts. Workers, sometimes called stringers, are sent to the sample precincts on Election Day. As soon as possible after the polling place closes, the stringer's job is to get the actual vote totals from the polling place officiai and call these results into a central location where they are tabulated and fed into computerized statistical models for analysis. Sometimes it is also possible to get the sample precinct votes via the Internet or by phone. The sample precinct models can take various forms, including ratio and regression estimators. For statewide elections, a typical sample size for this purpose is about 80 precincts and usually varies from 15 to 100 depending on the characteristics of the state, the newsworthiness of the electoral contest, and how close the election is expected to be.

The second use of precinct samples is for conducting Election Day exit polls, such as those conducted for the National Election Pool by Edison Media Research each major election year since 2004. The exit poll precinct sample is usually a smaller subset of the sample used to collect the actual vote tallies. A typical statewide exit poll will have about 30 sample precincts and typically ranges from 15 to 60. Exit poll interviewers are sent to the sample precincts to interview voters as they exit the polling place. Data are collected on voters' demographics and opinions and how they voted. These data are called into a central location three times during the day and tabulated. The demographic and opinion data are cross-tabulated with the vote and are used to analyze why voters voted the way they did. These data help explain why candidates won or lost and what issues were important to voters. The data from the exit poll sample precincts are also used to help project the election outcomes.

...