The early returns yesterday -- from focus groups, pundits, and snap surveys -- indicated that John F. Kerry had a good night when he faced off against President George W. Bush at the University of Miami. But public opinion specialists say it is by no means certain that conventional wisdom and poll numbers taken in the first hours after a presidential debate will correctly forecast the winner on Election Day.
''In terms of who won, I don't think that's a terribly predictive factor in the race itself," said Karl Agne, a senior adviser at Democracy Corps, a nonprofit organization founded by Democratic strategists that conducted a poll indicating Kerry bested Bush in the debate.
Writing on the ABCNews.com website, Gary Langer, the director of the ABC polling unit, recalled only one debate -- Ronald Reagan's 1980 encounter with Jimmy Carter -- after which ''the lead changed hands by a meaningful margin. . . . Measurable effects show that debates, at least in immediate reactions, mainly tend to reinforce preconceived notions rather than change them."
The instant polls that fueled the media postmortems yesterday did contain good news for Kerry. The Democracy Corps survey indicated that 45 percent of the respondents said they felt the Democratic challenger had won the debate, compared with 32 percent who gave the nod to the incumbent.
A CBS snap poll of uncommitted voters, an American Research Group survey, a CNN/ USA Today Gallup poll, and an ABC poll all indicated that debate viewers, by solid margins, said Kerry had done a better job than Bush.
But the history of snap polling indicates that a number of candidates who were initially viewed as debate victors did not necessarily fare well at the ballot box.
In the 1984 campaign, a Gallup snap poll found that Walter Mondale had trounced Reagan in the first debate and CBS News director of surveys Kathy Frankovic recalls that Mondale cut Reagan's lead in half in the aftermath of that encounter. But Reagan recovered in the second debate and ultimately won in a landslide.
In 1992, Ross Perot was deemed the winner in two of three debates but finished behind George H.W. Bush and Bill Clinton on Election Day.
With a month until the election -- with two more presidential debates, plus the vice presidential debate Tuesday -- both campaigns have time to try to alter public opinion. New ads, new attacks on the candidates' records, and unforeseen events can become factors with voters between now and Nov. 2.
When questioners asked respondents for their presidential preference before and after the Thursday debate, there was negligible change in the shape of the overall Kerry-Bush contest.
Dick Bennett, president of the American Research Group, said he generally thinks debates can influence presidential contests, but added that ''this year is different because the [number of undecided voters] is so low. It's culturally unacceptable to be undecided in this race."