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Even before the final balloons fell on the Republican and Democratic conventions, pundits were talking up the next big American political viewing experience — the presidential debates.

These match-ups, in which candidates actually share a stage after months of bruising one another from far range, can lead to moments of rhetorical brilliance, or the opposite — getting caught off-guard and making a gaffe.

Historically, debates have been seen as potential "game changers" in tight races. But political scientist John Sides, writing in the Washington Monthly, claims that data tells another story. Writes Sides.

"That presidential debates can be 'game changers' is a belief almost universally held by political pundits and strategists. Political scientists, however, aren't so sure. Indeed, scholars who have looked most carefully at the data have found that, when it comes to shifting enough votes to decide the outcome of the election, presidential debates have rarely, if ever, mattered."

Sides, an associate professor of political science at George Washington University, continues:

"The small or nonexistent movement in voters' preferences is evident when comparing the polls before and after each debate or during the debate season as a whole. Political lore often glosses over or even ignores the polling data. Even those who do pay attention to polls often fail to separate real changes from random blips due to sampling error. A more careful study by political scientist James Stimson finds little evidence of game changers in the presidential campaigns between 1960 and 2000. Stimson writes, 'There is no case where we can trace a substantial shift to the debates.'""At best, debates provide a 'nudge' in very close elections like 1960, 1980, or 2000. A even more comprehensive study, by political scientists Robert Erikson and Christopher Wlezien, which includes every publicly available poll from the presidential elections between 1952 and 2008, comes to a similar conclusion: excluding the 1976 election, which saw [President Jimmy] Carter's lead drop steadily throughout the fall, 'the best prediction from the debates is the initial verdict before the debates.' In other words, in the average election year, you can accurately predict where the race will stand after the debates by knowing the state of the race before the debates. Erikson and Wlezien conclude that evidence of debate effects is 'fragile.'"

Debates do help voters learn new information, but what voters learn is unlikely to change many minds, Sides writes.

Debates tend to draw the politically inclined who already favor one party or the other, some political scientists argue. And timing is also a factor. The televised sparring happens so close to Election Day that in several states, early in-person voting will have started before even the first debate.

Even so, expect the three televised presidential debates (and one vice presidential faceoff) to draw millions of eyes. Each general election cycle, the debates are among the most watched television programs of the campaign season, and this year will certainly be no different.

Latest polls show President Obama and Republican Mitt Romney continue to engage in a tight race less than eight weeks before the Nov. 6 election.

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