How do people predict/declare results with just little data.?

Question

well actually..i was watching the results of the pennsylvania poll between Clinton and Obama, and with just 12% of the total votes, this news people declared that clinton have won. i just wanna know how. its something to do with statistics

Answer 1

correct, it's something to do with statistics.  probability theory allows us to sample a relatively small number of cases and project those results to the larger universe with a defined range of error (+ or - a % of the end result).  it's obviously impractical to include everyone in surveys, but we can talk with just a few hundred or thousand (depending on what level of detail we need) and fairly accurately talk about all Americans.

separate, however, is the ability or inability of polls to predict actual behavior.  just because someone says they would today vote for X doesn't mean they will actually do so.  and surveys are notoriously bad at predicting future behavior.