There has been a lot of quibbling in this election about the samples of polls.Most noticeably Republicans and Democrats are complaining about the partisan breakdown and likely voter screens in major national surveys. But Barreto makes an important point that has two key implications. One, many Latino voter spreads from national polls are based off poor data and get publicized and fetishized. Two, in certain polls, Latino voters could be undercounted, which could lead to Obama's overall support being understated.
Barreto uses a recent Monmouth University poll as an example, which shows Romney leading Obama 48-45 percent. In the poll, Obama only leads among Latino voters 48-42 percent. That amounts to a six point lead. But in fact, national polls that focus on Latino voters with large samples conducted in English and Spanish show Obama with an average lead of 48 percentage points over Romney.
Here is what Barreto says it might look like if that margin was factored into national samples:
Let's examine how these faulty Latino numbers create problems with the overall national estimates. Afterall, 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 represent an estimated 17 percent of all voters. If you are badly mis-calculating the candidate preference among 17 percent of the electorate (that's 1 out of every 6 voters), then the entire statewide estimates are wrong.
As Jamelle Bouie of the American Prospect notes, it's entirely possible for national polls to get the horse race right without correct demographic samples. Also, don't forget that polling has consistently showed enthusiasm among Latino voters and other minority groups lagging behind that of the general electorate, meaning that turnout could fail to meet expectations in 2012.
But Barreto correctly points out that undercounting Latino voters and African-American voters in polls may distort the true state of the race. That's hugely important in a campaign where the electorate is highly polarized down racial lines with white voters backing Romney by large margins and nonwhite voters rallying behind President Obama.
Check out Barreto's full statistical analysis here.