The consortium of news media formed to obtain exit poll data on Election Day acknowledged Wednesday that the data dramatically overstated the percentage of voters who supported Democrat John Kerry.

It also announced steps to prevent the leaking of preliminary exit poll data in future elections.

"The exit poll estimates in this year's general election in many states and in the national survey had a sizable overstatement of the estimated percentage of the vote for John Kerry," said a report by Edison Media Research and Mitofsky International, the research firms that conducted the polls.

Edison and Mitofsky were hired to do the polling by the National Election Pool, which comprises the major broadcast and cable news networks and The Associated Press.

Poll data to be delayed

The NEP said that in future elections it will not release exit poll results to members and subscribers until 6 p.m. Eastern time to minimize leaks.

Early exit poll results circulating on the afternoon of Nov. 2 heavily favored Kerry, leading some television commentators to hint at a victory for the senator over President Bush. Though the data are supposed to be kept confidential until polls close, they leaked onto many Internet sites almost as soon as they were released to members early in the afternoon.

The eventual Bush victory led many to question the reliability of exit polls and the wisdom of conducting them at all, particularly in light of the fiasco of the 2000 election when flawed exit poll data contributed in part to botched calls by news outlets.

The networks initially defended the polls, saying that early results were preliminary and never intended for release. They said the final numbers distributed later on election night were more accurate.

But Wednesday's report confirmed that in the case of 26 states and the nationwide exit poll, the final results skewed in Kerry's favor.

"Even when the polls were complete, we were overstating the Democrat," said Warren Mitofsky, president of Mitofsky International. The final nationwide exit poll, which was completed at 11 p.m. EST on Nov. 2, showed a Kerry victory with 51 percent of the vote to Bush's 48.

Mitofsky said exit polls have always tended to give an edge to Democratic candidates, and that he had anticipated the problem and taken steps to account for it. But he said the magnitude of the discrepancy was greater than he had expected. He said that for reasons that remain unclear, Democratic voters are more likely than Republicans to agree to interview requests from pollsters.

Pollster defends practice

Mitofsky and network election experts acknowledged that more needs to be done to refine the exit-polling system, including better recruitment and training of pollsters, but insisted that the practice is sound.

"They run a professional operation, and they know what they're doing," said Tom Hannon, the political director for CNN, a member of the pool. "They didn't make one bad call. There were problems, but compared to 2000, they weren't that bad."

Critics pounced on the NEP report.

"I'm not sure that I will ever believe an exit poll again," said John Zogby, president and chief executive of the polling firm Zogby International. "How could they have been so way off? They were worse than virtually every pre-election poll." Zogby's pre-election polling predicted that Kerry would win.

But Kathleen Frankovic, director of surveys for CBS News, also a pool member, said she supports exit polling but said it is not surprising that the exit polls were off because all polls are estimates rather than vote counts.

"If you want to do an exit poll, there's a lot of detail and a lot of potential for problems," she said. "Maybe this will undercut some of the blind faith in exit polls."

Mitofsky laid most of the blame for the Election Day confusion on people who distributed the data on the Internet.

"I don't really take well [to] being criticized for numbers that were leaked when I didn't leak them," he said.