At the moment, Newt Gingrich is slightly ahead in Alabama while Mitt Romney has a narrow edge in Mississippi. But numbers wizard Nate Silver thinks that polls from southern states are less reliable than elsewhere and that therefore, it's still anyone's race in those two states.

If you had looked at the Real Clear Politics average of polls in Alabama in advance of the 2008 primaries, for instance, you would have called the Republican and the Democratic races wrong. Hillary Rodham Clinton had a nominal advantage in the Democratic race there, leading in the Real Clear Politics average by about one percentage point. But in fact, Barack Obama won. It wasn't even close; he carried the state by 14 percentage points.

A similar problem was evident on the Republican side. The polls were wildly divergent from one another - showing everything from a 16-point lead for Senator John McCain to a 9-point advantage for Mike Huckabee. But the average put Mr. McCain about four percentage points up in Alabama. Mr. Huckabee won the state by about four percentage points instead, however.

Alabama and Mississippi haven't played an important role in primaries that often, but in one important prior case - the Democratic race in 1984 - the polls were also pretty bad there. Surveys substantially overestimated Walter Mondale's standing - one survey had him with as much as 48 percent of the vote, but he got just 35 percent. They had Gary Hart finishing about 10 percentage points ahead of Senator John Glenn for second place, when the two candidates about tied for second. And Jesse Jackson did substantially better than was forecast for him by the polls.

Why is this? Silver attributes the problem to what pollsters refer to as "social desirability bias:"

Polls can sometimes have problems because of social desirability bias - the tendency to provide an answer that you think might seem most acceptable to the stranger on the other end of the line, rather than what you really think.

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Etiquette also remains more in tact in the South, and especially in the Deep South, than in most other parts of the country. If so, polls there could encounter similar problems.

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If the causal mechanism is social desirability bias, however, it might be that the polls exaggerate the standing of candidates who are seen as more broadly acceptable and as less offensive, or who have the support of the establishment. In this election, that might be Mr. Romney, who won the endorsement of Gov. Phil Bryant of Mississippi.

This makes some sense. If it proves right, Newt Gingrich should have a very good night and Mitt Romney will have more questions about his viability as a candidate.