Can Election Probabilities Be Established at This Point?

[Nicholas_J]

Labor Day to Election Day patterns from past elections help put the current situation in context

GALLUP NEWS SERVICE

PRINCETON, NJ -- The fundamentals of the presidential race did not change dramatically as a result of the Republican convention. George W. Bush had a slight lead over John Kerry among likely voters prior to the convention. He has now edged further ahead.

A question of keen interest to election observers focuses on the possibility of significant or dramatic change from this point forward. Bush is ahead of Kerry by seven points among likely voters. What is the probability that Kerry can come from behind and win the election?

"Gap Changes" Between Labor Day and Election Day

There have been 17 presidential elections since Gallup's election polling began in 1936. In each instance we can look at the difference in the margin between the Gallup Poll that immediately followed Labor Day and the final popular vote outcome...

Bush has a seven-point lead over Kerry at the Labor Day juncture. In about half of all past presidential races, the election dynamics have shifted so that there was a change of at least seven points in the gap between candidates' vote percentages by the time of the election. Thus, in a broad sense, there is historical precedent that races can change to the extent necessary for Kerry to erase Bush's lead. In six out of eight cases, gap changes are in the direction of shrinking rather than expanding margins, which would also work in Kerry's favor.

At the same time, there are only 2 examples (1948 and 1980) out of the last 17 elections that fit exactly the circumstances Kerry needs if he is to win: a gap change of at least seven points and a lead change from Labor Day to the election. Two other races -- in 1976 and in 1968 -- came close to these specifications (with the Labor Day leader barely holding on to win). Thus, of the last 17 elections, 4 can be said to have demonstrated the type of Labor Day to Election Day change that would be necessary for Kerry to win this year.

Finally, it is important to note that even with 17 elections, we are dealing with a limited set of cases for precise statistical modeling. Polling techniques have changed over the years, and other changes in the ways poll estimates were made since 1936 mean the comparability of situations across the years is not exact. Nevertheless, it is instructive to use the historical data to provide the best possible empirical basis for assessing election probabilities. Otherwise, such assessments are left to speculation and informed guessing.



http://www.gallup.com/poll/content/?ci=12970

Basically the article goes on to note that in all of the elections between 1936 and 2000, the gap between the candidate in the lead and the candidate behind has always narrowed, and that on average, the number of percentage points that the polls narrowed to by election day was 7 points, which is the number of point that Gallop has Bush ahead, indicating that by election day, Kerry will narrow the gap between himself and Buch to where the election will be virtually equal.

[FARAFIELD]

1. JUST FOR THE RECORD

I dont know why the press has run the story that the lead is "7" when it is really "1" look at the polling reports! the lead in registered voters is "1"!!! not 7. Besides that the zogby is much closer and he used a better base for his sample.