Two new surveys out this morning, from the Des Moines Register and NBC News, show Newt Gingrich with the polling lead for the Iowa Republican caucuses. Although these results are broadly in line with other recent polls of the state, it is good to get the confirmation since these are extremely high-quality surveys. On average, Mr. Gingrich is at 25 percent in the two polls, with Mitt Romney and Ron Paul each at 17 percent.

But how safe is an 8-point polling lead a month in advance of Iowa?

The obvious way to get some impression of this is to review what the polls looked like a month in advance of past caucuses. That’s what I’ve done in the table below. It lists the results from polls of past Iowa caucuses dating back to 1980, excluding 1992 when neither party’s caucus was competitive. The numbers in the chart represent the average of all polls conducted from three to six weeks prior to the caucuses, with the exception of 2004 when this period coincided with the holidays and I had to expand the window slightly to find any surveys.

Of the 11 competitive caucuses since 1980, the candidate leading in the polls a month in advance won them 8 times. That’s a pretty good batting average for Mr. Gingrich. As difficult as it is to poll the caucuses, surveys of Iowa have tended to be pretty reliable in the past.

It is important to note, however, that Mr. Gingrich’s lead is smaller than that of most candidates from past years. In the five prior cases where a candidate had a single-digit lead, he won twice but lost three times. The losses came in 1980, when Ronald Reagan lost to a better-organized candidate in George H.W. Bush, in 1988, when there was an essential four-way tie in the Democratic caucuses and the nominal leader, Gary Hart, lost to Richard Gephardt, and in 2004, when Howard Dean’s support collapsed and he lost to John Kerry.

Perhaps Mr. Romney can take solace from the comeback of Mr. Kerry, a candidate to whom he is sometimes compared. One might also be able to make a superficial comparison between Mr. Gingrich and Howard Dean, as both candidates are relatively brash and bombastic.

Then again, one thing that helped Mr. Kerry in 2004 was the collapse of Mr. Gephardt’s numbers in addition to Mr. Dean. Mr. Gephardt and Mr. Kerry were both fairly traditional candidates with their share of endorsements from unions and other Democratic groups, so Mr. Kerry was a logical candidate for Mr. Gephart’s supporters to turn to once he embarked upon an unappealing feud with another candidate, Joseph I. Lieberman.

By contrast, the other candidate to poll in the double-digits this time around is Ron Paul, who tends to attract his own breed of supporters and not the kind who would be inclined to vote for Mr. Romney. Nor is there any reason to think that Mr. Paul’s numbers will collapse. Instead, he has been gaining ground in Iowa and has a very strong organization there, which often allows a candidate to over-perform his polls on election day.

If I were setting odds as of this morning, I might assign Mr. Gingrich about a 45 or 50 percent chance of winning Iowa, followed by Mr. Paul at 25 percent and Mr. Romney at 15 percent, reserving a small possibility of a comeback by Rick Santorum, Michelle Bachmann or Rick Perry. Of course, much of this has to do with what you think about the robustness of Mr. Gingrich’s campaign overall and not just his Iowa polls. There are three debates in Iowa between now and the caucuses, which will undoubtedly go a long way toward determining the winner.

We can also take a quick look at what the New Hampshire polls looked like a month in advance of the Iowa caucuses. Mr. Romney now has about a 16-point lead in New Hampshire, although it has been shrinking. Note that the table below does not include 1980, as there weren’t very many New Hampshire polls that year until after the Iowa caucuses were conducted.

The New Hampshire polls have historically been a pretty rough guide this far out from the primary. Of the past 11 candidates to hold a lead in New Hampshire at a comparable point in the cycle, only 5 won. In some cases, like that of Walter Mondale in 1984 or Howard Dean in 2004, the candidate lost despite having a lead in excess of 20 or 30 points. Meanwhile, candidates have come back to win New Hampshire despite being as low as 5 percent (Gary Hart in 1984) or 10 percent (Pat Buchanan in 1996) in the polls. Thus, New Hampshire would still appear to be fairly wide open. Mr. Romney is the favorite in the state, but Mr. Paul, Mr. Gingrich and Jon M. Huntsman Jr., who has been gaining ground in recent surveys, also have plausible chances there.