Poll aggregator

A poll aggregator is a web site that predicts upcoming U.S. federal elections by gathering and averaging pre-election polls published by others. The site predicts the winner of a presidential election and post-election composition of the Senate and House of Representatives, as well as showing who is currently ahead where and by how much. It is useful in U.S. presidential elections because the presidency is determined by the winner of state by state elections (see Electoral College), and not by simple popular vote of the entire nation. Editorial commentary by the site's owners and others complements the data. Interest and web traffic peak during the last few weeks before the election.

How individual polls are averaged varies from site to site. Some aggregators weight polls in the average based on past pollster accuracy, age of the poll, or other more subjective factors. The averaging method has been criticized by at least one statistician because it doesn't weight them by sample size. In this way the resulting average support percentages do not reflect the actual support percentage for any candidate of the pooled polls.