July 24: The Incredibly Steady Presidential Race

By NATE SILVER

We've now been running our presidential forecast model for almost two months, but very little has changed in our analysis of the race. Each day, we have shown Barack Obama as a modest favorite to win re-election. At no point has projected margin of victory in the popular vote been smaller than 1.7 percentage points, or larger than 2.7 percentage points; it was 2.3 percentage points as of Tuesday evening's forecast.

The “now-cast” - our estimate of what would happen if the election were held today, rather than on Nov. 6 - has been only slightly more volatile. Mr. Obama has led in each now-cast as well, but by margins ranging from 0.9 points (on June 21) to 2.9 points (on July 21). As of Tuesday, the now-cast gave Mr. Obama a 2.6 point lead.

As has often been the case, the two new data points that had the most influence on Tuesday's forecast contained good and bad news for each candidate. The good news from Mr. Obama's point of view was a new NBC News / Wall Street Journal poll gave him a 6-point lead in the national horse race. It's a good number for Mr. Obama - NBC News / Wall Street Journal is a strong pollster that tends to play it straight up the middle.

Still, it's just one data point from among many, and there just isn't any evidence that the race is breaking toward either candidate. (In contrast to the NBC data, for instance, the weekly tracking poll conducted by Public Policy Polling for Daily Kos showed Mr. Romney pulling into a tie with Mr. Obama for the first time in the survey.) These polls, and almost all others within the past few weeks, are consistent with an essentially unchanged race in which there is some statistical variation from survey to survey, and some differences introduced by the different methodologies that pollsters apply - but perhaps not a whole lot more going on beyond that.

Meanwhile, the stock market fell sharply for the third consecutive trad ing session on Tuesday. Investors are concerned about the credit situation in Europe. But frankly - although I don't mean to give stock market advice - the market has had a relatively optimistic reaction to decidedly mediocre data from the American economic ticker in recent weeks. With the recent downturn, it is falling closer into line with the six other variables that make up our economic index.

We're not yet at the point where the economic index sees Mr. Obama as an underdog for re-election - it should be remembered that incumbent presidents tend to get quite a lot of credit from voters - but it does see an extremely close race and is exerting some slight downward pressure on his forecast. That is why Mr. Obama's margin over Mr. Romney in the Nov. 6 forecast - which accounts for economic factors along with polls - is slightly lower than his now-cast, which is based on the polls alone.

Mr. Obama's chances of winning the Electoral College on Nov. 6 were 65.9 per cent as of Tuesday's forecast, down slightly from 66.9 percent on Monday.