One of the most anticipated events of every presidential election cycle are the debates. In recent years, they have become institutionalized, but they are a relatively new phenomenon. The first was the famous Kennedy-Nixon debate, and there would not be another one until 1976, when they became a permanent fixture. Debates are unscripted, and with tens of millions of viewers they are the biggest collective experience voters will have in making a choice.

But it’s rare a debate will change the course of the election. The 1960 debate is part of American political lore, with Kennedy’s dashing appearance and Nixon’s haggard look affecting perceptions over who won the debate. In spite of this, the race was close the whole way through, and Kennedy received no bump from winning the debate.

In more recent times, there has been little evidence that debates have had an impact on the race. In 1992, George H.W. Bush had a well-known gaffe, where he would look down at his watch while he was onstage. This was supposed to demonstrate how out of touch he was. And yet, Bush continued an upward surge in the polls after this. Bush had been trailing by 20 points in the summer but made up ground in September and October and nearly tied the race with a week left.

Al Gore was widely acknowledged to have an awkward first debate performance, between his audible sighs on stage and a truly odd stare-down of George W. Bush. The polls did show an immediate spike for Bush, but the tracking for Gallup was incredibly volatile in October 2000, with both Bush and Gore having double digit leads at some point in the month. Even if Bush received a boost, it was not long lasting.

In 2004, President Bush came into the debates with a head of steam from a convention bounce. However he had a weak first debate, and polls showed that a high single-digit lead evaporated. This could have been a game changer, but Bush was able to recover in the other two debates, and he was able to retain a small but real lead until Election Day.

The 2008 presidential race was conducted in an unprecedented atmosphere, where financial institutions were on the brink of collapse. In such an environment, the importance of the debates was lessened. The updraft that Obama received in late September and October had little to do with the debates and much to do with events occurring in real-time.

Has a debate ever changed the course of an election? Certainly yes, one time or another case, it is arguable. In 1976, Gerald Ford had trailed Jimmy Carter by 30 points as late as July of that year, but he made up enough ground that after the first debate he was able to tie it up. In the second debate, Ford made a terrible error when he claimed that Eastern Europe was not under Soviet domination. This was costly because Carter was able to take a small lead for the rest of the contest. In a close election, Ford could have won if he did slightly better in Ohio and Wisconsin—two states with large populations of Americans with Eastern European ancestry.

The one time a debate clearly changed a race was in 1980. Due to arguments over the involvement of third party challenger John Anderson, Carter and Reagan were only able to agree to one debate. This sole debate was held on the last Thursday night of October—five days before the election. This was the most-watched presidential debate in history, and Reagan was viewed by most as the clear winner. President Carter’s pollster Pat Caddell had the race tied going into the final weekend, but Reagan was up seven to 10 points by the day before the election. The unique circumstances of this debate are what made it a decisive campaign event.

There is evidence in recent years that candidates can have a boost based on debate performance, but no set of debates in the past 30 years have actually decided an election. And now that the presidential debates have settled into a pattern of three debates, starting about a month before the election, the odds that one debate this year drastically changes the race is unlikely.

Chris Palko works as an assistant media analyst at Smart Media Group, a Republican political media buying agency in Alexandria, Va. He is a graduate of American University and George Washington University’s Graduate School of Political Management.

A version of this post was also published on Smart Media Group’s blog, Smart Blog.