Special Report: U.S. presidential election 2008    

    WASHINGTON, Oct. 2 (Xinhua) -- U.S. vice presidential (VP) candidates Joe Biden and Sarah Palin will debate at Washington University in St. Louis, Miss., Thursday night.

    It is be the first such debate to feature a female candidate since the 1984 vice presidential debate.

    The first ever U.S. VP debate was also held in 1976 between Democratic Senator Walter Mondale and Republican Senator Bob Dole.

    Since then, there will be one debate between VP candidates every four years.

    Although there has been no evidence that a VP debate ever changed the outcome of the general election, some analysts also pointed out that the performance of VP nominees affects the evolution of swing voters' attitudes toward the presidential nominees during the campaign.

    Especially, in a close election like this year's, VP nominees can offer reassurance to --or raise new doubts among-- voters who are still making up their minds.

    For example, the first ever VP debate between Bob Dole and Walter Mondale in 1976 may have had the biggest impact on a presidential race's outcome.

    Dole had been tapped by Gerald Ford to appeal to conservative Republicans and to shore up heartland states for the GOP ticket.

    But he showed none of the good humor for which he later became known on the campaign trail, instead earning a reputation for nastiness and mean-spiritedness.

    The Ford-Dole ticket was on the move when the VP debate was held, having cut a 33-point deficit into single digits.

    But Dole created a severe headache for the ticket and slowed its momentum when he answered a question about Watergate by declaring: "I figured out the other day: If you added up the killed and wounded in Democrat wars this century, it would be about 1.6 million Americans enough to fill the city of Detroit."

    His debate opponent Mondale simply responded: "I think Senator Dole richly earned his reputation as a hatchet man," a characterization that would haunt Dole for the years to come.

    Ford ended up catching Jimmy Carter over the final weekend, only to watch Carter surge ahead in the final three days and win by two points.

    The debate between Joe Biden and Sarah Palin is the most anticipated since 1984 for two reasons.

    One is that the presidential race is close and the public is unusually engaged.

    But the bigger reason is the unpredictability of both candidates.

    Palin has humiliated herself in a series of interviews with Katie Couric and Charlie Gibson, confirming suspicions that she lacks even a basic grounding in some key policy issues.

    As a result, the bar has been lowered so much that even an average performance from Palin will be greeted by voters as a pleasant surprise.

    Biden, for his part, has a reputation for loquaciousness. His critics had questioned his self-control and set the bar low for him, too.