Guest Pollster | October 1, 2006
Topics: 2006 , Likely Voters , The 2006 Race
Editor's Note: This post inaugurates a new feature on Pollster, our "Guest Pollster's Corner." We hope this new forum will provide opportunity for professional pollsters of all stripes -- media and campaign; Democrat, Republican and non-partisan -- to occasionally share their own thoughts on the art and science of political polling. We are honored to receive our first contribution from Frank Newport, the Editor and Chief of the granddaddy of them all, the Gallup Poll.
The average turnout level among the voting age population in midterm elections is typically well below 50%, significantly lower than in presidential election years. This means by definition that the actual group of voters who turn out and vote on Election Day is a relatively small sub-set of the large poll of all eligible voters. If there is no difference in the voting intentions between these two groups, then reports of pre-election generic ballot results based on registered voters are all that is needed. If the pool of those who have the highest probability of voting is significantly different from those who are less likely to vote, however, then the effort to identify likely voters in pre-election polls becomes critical to accurately predicting and understanding the outcome.
Gallup's past history of polling indicates there is a high probability of a significant difference in the voting intentions of the large pool of registered voters and the smaller subset of likely voters in lower turnout midterm elections.
In 1994, Gallup's final generic ballot showed a dead heat between the Republicans and Democrats among all registered voters, but a 7-point lead for the Republicans among likely voters. According to estimates of the national-two party vote for that election, the Republicans had a nearly 7-point advantage in all votes cast for Congress that year (52.4%-45.5%). (In the penultimate Gallup poll in late October 1994, the likely voter "gap" showed a 10-point Republican advantage, while the registered voter gap in the same poll showed a 3 point Democratic lead, representing a 13-point difference in the gap between the two groups.)
In 2002, Gallup's final generic ballot among registered voters -- in the poll conducted Oct 31-Nov 3, 2002 -- showed a 5 point- Democratic edge, 49%-44%. Among likely voters it was 51% to 45% Republican, for a difference in the gap between registered and likely voters of 11 points. The final national House vote in 2002 was 50.5% for the Republicans vs. 45.9% for the Democrats, a 5 point Republican advantage).
In both of these years, the distinction between the vote intentions of all registered voters and likely voters was significant. The likely voter estimate was more predictive of the real world outcome.
Gallup's first use of the likely voter model in 2006 -- in the USA Today/Gallup Poll conducted Sept 16-17 -- provided an early suggestion that the standard pattern of turnout by party will continue this midterm cycle. Among the pool of all registered voters in the sample, Democrats led Republicans by a 9-point gap, 51% to 42%. Among the pool of those identified as likely voters, the ballot was tied at 48% to 48%.
This can change during the course of the election between now and Nov. 7. Likely voter estimates are more volatile than estimates based on larger samples of registered voters or all national adults. The gap between registered voter and likely voter estimates often fluctuates in September and October, particularly in response to the high-intensity campaigning likely to occur over the next month. Still, the mid-September Gallup results suggest that the historical turnout advantage Republicans have enjoyed in mid-term elections appears to be operative again this year -- at least as of this point.
Editor in Chief, The Gallup Poll