Voter News Service, a cooperative of The Associated Press, ABC, CBS, CNN, NBC and Fox news networks conducted its national exit poll in Tuesday's elections by interviewing 9,900 voters as they left polling places in about 1,150 precincts nationwide.

The national poll sample was drawn from samplings in each state. Each poll precinct was picked randomly in a process that was ordered to reflect national geography and past vote by party.

As people left voting booths, VNS interviewers asked them to fill out a confidential questionnaire. Voters were chosen at a set interval _ such as every fifth person _ so that each voter had an equal chance of being picked.

The results were adjusted to reflect the different probabilities of selecting a precinct and a voter within each precinct, as well as the observed sex, race and estimated age of voters who refused to participate.

As with any poll, the results could vary because of chance variations in the sample. For this poll, there was one chance in 20 that sampling error would cause the results to vary by more than 1.5 percentage points either way from the opinions of all voters who participated in the elections. The error margin was higher for subgroups in the sample.

Polls are subject to other sources of error, such as from question wording or order.