Well under way this year is the quadrennial pre-convention guessing game of estimating how public opinion polls will move after each of the weeklong summer rallies hosted by the political parties.

The "convention bounce" (search), a phenomenon pollsters and pundits have been talking about for decades, fulfills the expectation that the presidential candidates will experience a temporary uptick in their popularity polls following the days of free, positive attention during the party conventions.

John Kerry will get a boost after the Democratic Party's convention in Boston next week and President Bush will gain some momentum in the polls after the GOP's pre-Labor Day convention. Both parties will try to play down expectations so as to exceed them.

Still, party officials are hoping that strong performances by their candidates during the four-day conventions will have effects lasting to the November election.

Those hopes may be dashed this year, however. Several pollsters say that Bush and Kerry are unlikely to see significant gains because few undecided voters are out there.

"In this closely divided electorate, it is probably unrealistic to expect Bush or Kerry to get much of a bounce," said American Enterprise Institute (search) polling expert Karlyn Bowman.

"There's an intensity level here early on that is unprecedented," said Scott Rasmussen, president of Rasmussen Reports (search), who added that the country is very politically polarized and mounds of cash have been spent early on in the campaign season.

"This election is primarily going to be determined by what happens in the real world — the economy and Iraq — not by the campaign," he said.

Bowman calculated that since 1964, candidates have enjoyed an average bounce of six points. Rasmussen cautioned, however, against looking at historical numbers since different methodologies and timings can skew the results.

However, comparing the Gallup Poll (search) against itself may provide some perspective. According to Gallup, in 2000, Democrats received an 8-point jump; Republicans got a 4-point boost. In 1996, Democrats went up by 5 points, and Republicans by 3. In 1992, Democrats shot up by 16 points, and Republicans gained 5. In 1988, Democrats gained 7, and Republicans 6.

Acknowledging the difficulties in comparing poll numbers from different organizations and in different years, Rasmussen computed the average bounce as mid to high single digits.

Pollsters do recall two conventions that were unusually significant — the 1988 Republican and 1992 Democratic conventions. In 1988, George H.W. Bush introduced the line "Read my lips: No new taxes," which became an important and powerful theme in his campaign.

In 1992, Bill Clinton enjoyed a huge jump in the polls following the Democratic convention. He wowed the crowd with his speech and very effectively used a video biography, where the audience learned that he came from "a place called Hope."

"The Clinton biography was considered legendary for really impacting viewers at home," said Todd Weiner, associate project director for Luntz Research (search).

The party conventions will give each candidate several hours of prime-time broadcast television coverage and wall-to-wall coverage on cable news channels. However, the parties are likely to be preaching to the choir, say pollsters.

"Most of the people that you need to persuade are not going to watch the conventions," Rasmussen said.

As pollsters make their predictions, the two camps have been trying to manage expectations so as not to throw off their post-convention strategies.

In a July 5 statement, Matthew Dowd, chief strategist for the Bush campaign, tried to create the highest expectation for Kerry after the Boston convention by combining the expected Democratic boost with the commensurate drop by the Republicans as well as factoring in the choice of John Edwards as the vice presidential candidate.

"An examination of Gallup polls in presidential elections since 1976 reveals that a challenger's vice presidential selection and nominating convention can have a dramatic (if often short-lived) effect on the head-to-head poll numbers. In fact, historical analysis suggests John Kerry should have a lead of more than 15 points coming out of his convention," Dowd said.

If Kerry does have a huge bounce, the Republicans can write it off as expected, however, if his bounce is somewhat smaller, it will look like a defeat, Allison Dobson, spokeswoman for John Kerry for President, said, explaining Dowd's attempts to maximize Kerry's expected gain.

But Christine Iverson, spokeswoman for the Republican National Committee (search), said that the Kerry campaign's attempts to lower expectations are also unrealistic.

"Both parties see a bounce when you have such attention, such coverage of your candidates. For the Kerry camp to be lowering expectations is simply not accurate," Iverson said.

Regardless of the size of the increase, all sides agree that any boost should not be expected to last.

"Kerry will be up when he leaves Boston. Bush will be up after he leaves New York. After that, nobody knows," Weiner said.