In the most recent national poll from Monmouth University, Mitt Romney leads President Obama by three points, 48 percent to 45 percent. If you dip into the internals, however, you’ll see something odd: Obama has a small six-point advantage over Latinos, 48 percent to 42 percent. What’s unusual about this is that it runs counter to every other survey of Latino voters, which—on average—show Obama with a 48.4 percent lead over Romney among the group.
It’s possible that Monmouth’s result won’t matter much for the accuracy of the topline number—because of small sample sizes for particular groups of voters, a poll can still be accurate, even if it has an unusual demographic breakdown. But there’s room for disagreement, and as Matt Barreto explains in a must-read post at the Latino Decisions blog, this missampling of Latino (and African American) voters could have a hugely distortionary effect on perceptions of the presidential race. He explains:
Let’s examine how these faulty Latino numbers create problems with the overall national estimates. After all, Latinos are estimated to comprise 10% off all voters this year. If Latinos are only leaning to Obama 48–42, that +6 edge among 10% of the electorate only contributes a net 0.6 advantage to Obama (4.8 for Obama to 4.2 for Romney). However, if instead Obama is leading 70.3 to 21.9 that +48.4 edge contributes a net 4.8 advantage to Obama (7.0 to 2.2), hence the national polls may be missing as much as 4 full points in Obama’s national numbers. […]
If these mistakes are being made nationally where Latinos comprise an estimated 10% of all voters, they are even worse in statewide polls in Nevada, Florida, Colorado and Arizona where Latinos comprise an even larger share of all voters. In Florida Latinos are estimated at 17% of all voters. If you are badly mis-calculating the candidate preference among 17% of the electorate (that’s 1 out of every 6 voters), then the entire statewide estimates are wrong.
I highly recommend that you read the entire post. The main takeaway is that the polls might be underestimating Obama’s level of support, due to small and unrepresentative samples of Latino and African American voters. If that’s the case, then Obama’s position is much stronger than it looks.