If Nevada continues to be one of the handful of pure toss-up states, why the dearth of polls in the state, asks UNLV political science professor David Damore in PolitickerNV. “Two of the primary issues associated with polling in Nevada are the sporadic nature by which the polls are conducted and virtually all of the polling is done on the cheap, yielding small sample sizes and large margins of error,” Damore writes.

RealClearPolitics lists 15 presidential polls in Nevada since February; for comparison, fellow swing state Colorado has had 29 polls at last count.

The latest polls still show John McCain ahead, but on the ground Nevada’s starting to feel blue. With Democrats leading Republicans in registration by more than 76,000, why is the race still so tight — and McCain ahead — even in the few polls available in the state?

“The folks who end up in these samples tend to lean towards the old and reliable. In this case of Nevada, this means that those more likely to be sampled are those who regularly vote, hold stable addresses, and rely on landlines (e.g., rural voters who overwhelmingly favor the GOP),” Damore explains. In contrast, many of Obama’s most fervent supporters are “young, first time, cell phone only voters” who are difficult to reach by pollsters.

By the end of 2007, 15.8 percent of U.S. households were cell-only, more than triple the figure from just four years ago, according to government estimates. Though pollsters massage data with complicated weighting schemes, the rise of cell-only households poses a challenge. A 2007 report examining the cell-only problem by the Pew Center for the People & the Press sums up the challenge:

If people who can only be reached by cell phone were just like those with landlines, their absence from surveys would not create a problem for polling. But cell-only adults are very different. The National Health Interview Survey found them to be much younger, more likely to be African American or Hispanic, less likely to be married, and less likely to be a homeowner than adults with landline telephones. These demographic characteristics are correlated with a wide range of social and political behaviors.

And while a 2006 Pew survey concluded cell-only respondents answered similarly to landline users when asked about their party identification or if they’d vote for a generic Republican versus a generic Democrat, Pew’s 2008 surveys show a stark difference. Landline respondents were split down the middle, with 45 percent each choosing McCain and Obama. But the cell-only respondents favored Obama 55 to 36 percent. The most recent report concludes:

Traditional landline surveys are typically weighted to compensate for age and other demographic differences, but the process depends on the assumption that the people reached over landlines are similar politically to their cell-only counterparts. These surveys suggest that this assumption is increasingly questionable, particularly among younger people… Pew’s surveys this year suggest at least the possibility of a small bias in landline surveys. Such a bias could be consequential in an election that appears to be very competitive right now, especially if significant numbers of young people turn out to vote.

Is John McCain giving up on Nevada?

Yesterday, John McCain backed out of a planned appearance in Reno, meaning the Republican candidate hasn’t been to the Silver State since addressing the convention of Disabled American Veterans in Las Vegas August 9. Running mate Sarah Palin’s only stop in the state was her first solo campaign appearance at a rally in Carson City September 14. Obama was in Reno yesterday, and has made at least 4 stops in the state since McCain’s last visit.

Instead of trying his luck in Reno, McCain will make stops in Denver and Pueblo, Colorado, on Thursday and Friday. Since August, McCain has made 2 stops in Colorado while Obama has made at least 4, not counting appearances related to the Democratic National Convention.

Nevada is the only Battle for the West swing state where McCain has a slim lead in the polls. Obama continues to build his lead in Colorado and New Mexico.

Track the candidates campaign stops on Slate’s Map the Candidates.

Boulder Voter Registration

Judy DeHaas/Rocky Mountain News

Michelle Obama encouraged college students to register to vote at a rally at the University of Colorado in Boulder today. Both the Rocky Mountain News and Denver Post were liveblogging from the campus.

Liberal-leaning Boulder, where John Kerry beat George W. Bush by a 2-to-1 margin in 2004 countywide, is seeing a surge in voter registrations, with up to 2,000 new applications being received each day. County Clerk and Recorder Hillary Hall told the Daily Camera she expects up to 90 percent of the county’s 210,000 eligible voters to cast ballots.

Monday marks the deadline to register to vote in Colorado.