Attempt to measure public opinion by taking a survey of the views of a representative sample of the electorate; the science of opinion sampling is called psephology. Most standard polls take random samples of around a thousand voters, which gives results that should be accurate to within three percentage points, 95% of the time. The first accurately sampled opinion poll was carried out by George Gallup during the US presidential election 1936.
Opinion polls have encountered criticism on the grounds that their publication may influence the outcome of an election. Rather than simply predicting how people will vote, poll results may alter voters' intentions—for example, by establishing one party as likely to win and making the voters wish to join the winning side, or by making the lead of one party seem so great that its supporters feel they need not bother to vote.