Several polls of likely voters released last week show President Barack Obama with a lead over former Massachusetts Gov. Mitt Romney in the race for the White House. But both campaigns should keep something in mind: In recent years, "likely voter" polls have been consistently wrong in predicting victory margins.

Current likely voter methodology - which asks about past voting as well as intentions for the upcoming election - tends to undercount minorities, single women and younger voters. Polling all registered voters, as opposed to just those deemed likely to vote, is far more accurate.

This year, when the electorate is starkly divided on race and age and there's a growing gender gap, those mistakes could be significant. The issue isn't partisan advantage, but the accuracy of the information presented to voters.

In 2008, Gallup realized its likely voter methodology wasn't tracking the increased share of the vote that minority and younger voters would cast. Its likely voter data consistently showed Obama with only a 2 percent to 3 percent lead over Arizona Sen. John McCain. So Gallup's pollsters created what they called a "likely voter for 2008" sample, which showed Obama had closer to a 5 percent to 8 percent lead. Interestingly, this new criteria tracked Gallup's polling data for all registered voters - and Obama ultimately beat McCain by 7 percent.

In 2010, likely voter polls underestimated the minority vote, especially Hispanics, in key congressional races. In Nevada and Colorado, for instance, incumbent Democratic U.S. Sens. Harry Reid and Michael Bennet won despite end-of-campaign polls of likely voters showing them losing. Hispanic voters turned out in greater numbers - and were more supportive of Reid and Bennet - than those polls projected.

The increasing number of cellphone-only households and the fact that cellphone customers can keep their phone numbers after they move are posing challenges to polling accuracy. And these challenges are heightened in likely voter samples: Younger, single and minority voters are simply more mobile and less likely to have landline phones.

Polling data have become the main grist for the 24/7 media mill, from blogs to print to broadcast. So it's a problem if these data saturate the public with needlessly inaccurate information. The false perception of a Michael Bloomberg landslide in 2009, for example, thwarted challenger Bill Thompson's ability to generate meaningful coverage and funding in that New York City mayoral race.

It is long past time for the collective amnesia in the media regarding likely voter polling to be replaced with standards for projecting more accurate data to the public. The underlying polling data is sound, but the way it is projected is not.

Since polls of registered voters have been more accurate than likely voter samples, news media outlets should demand that both sets of data be provided (as Pew Research and the Siena polls, to their credit, do). And the media should give greater reporting weight to the more accurate polls of registered voters.

Pollsters pretending that they alone have a window on who is likely to vote is a fiction that should no longer be presented as a fact.

Bruce N. Gyory is a consultant with Corning Place Communications and an adjunct professor of political science at the University at Albany. He wrote this for Newsday.