How do politicians guess Election performance before the Results are announced?

Many political parties say they have done well or so and so party has not done well . On what %26amp; How are these predictions based ? . How are they able to guess the performance even before results are announced?|||After an election, an exit poll is published comissioned by the media covering that election. Using this information (as well as reports from the districts) a political panelist is able to make a good guess as to how they are doing.





For instance, at Election 2005 in the UK the exit poll suggested that the Liberal Democrats would gain two seats net and the Lib Dem spokesman was asked wether the last four years was a wasted chance. He replied: "Wait for Solihull!" Solihull was a Lib Dem gain from Con on a swing of 10% from Con to Lib Dem (and according to the exit poll should have stayed Con)|||exit polls|||What the person above me said.|||Political forecasts affects next day's polling.However political forecasts consists the contents as in the sales forecasts.