Gauging the Accuracy of Election Polls

Although polls have occasionally failed to predict who will win an election (most recently in the 2008 Democratic primary election in New Hampshire), polling’s track record is actually very good. The National Council for Public Polls has conducted analysis of presidential election polling accuracy from 1936 to the present and provides reports summarizing these results on their website.

The good track record of final pre-election polls does not mean that all pre-election polls are reliable. Polls conducted early in an election season should be taken as snapshots in time, and obviously cannot capture the impact of the campaign and events to come. This publication examines presidential election polls conducted well in advance of the election and attempts to gauge how predictive they are:

 

These publications provide a few tips to help in reading polls and deciding how much weight to give them:

 

National polls sometimes attempt to gauge how voters will vote in elections for the U.S. House of Representatives. Of course, there is no national election for the House; instead there are elections in each of the 435 congressional districts. But pollsters have found that the so-called “generic ballot test,” which asks whether respondents intend to vote for the Republican or the Democratic candidate in their local race for the House, can provide an accurate estimate of the vote on which projections about party gains and losses in seats can be based. The following publications illustrate the use of the generic ballot test and some of the issues involved in using it: