No economic indicator is a political holy grail. The American economy is a hard thing to measure, and initial estimates of economic performance are subject to significant revisions. Noneconomic matters — wars, candidates, scandals and so forth — matter, too.  But if you want to focus on a single economic indicator, job growth during the presidential election year has a lot going for it. The job-growth numbers do at least as well as any other economic number in predicting elections, and slightly better than some other commonly used metrics, like the gross domestic product.  So the news that the economy added 243,000 jobs last month was very good for President Obama. That pace is well above the minimum level — about 150,000 jobs — that he would seem to need to increase his chances of re-election.  Beyond the history, there are a lot of common-sense reasons to focus on the jobs numbers. They measure something tangible and important. They receive much attention from economists, investors, political campaigns and the news media, and therefore inform the public discussion. They are released every month after only a minimal lag. They are not subject to as much revision as some other economic numbers.  These qualitative factors are important because a sample size of 16 elections since World War II is insufficient for persuasive statistical evidence. But the statistical patterns are still striking.  In the three election years where the economy was actually shedding jobs, the incumbent party lost — badly in 1980 and in 2008, and in a close election in 1960. George H. W. Bush lost in 1992 when the rate of job growth was under 1 percent, below the rate of population growth.  On the flip side, in the election years when job growth was strongest — 1956, 1964, 1972, 1984, 1988 and 1996 — the incumbent party won the election fairly easily.  And in the three years in which growth was positive but modest — 1948, 2000 and 2004 — the races were close. A bit of common sense can explain these outliers. (Be wary of statistical analysis that substitutes data dredging for common sense.)  If Mitt Romney is the Republican nominee, the outcome does not seem likely to be an outlier. Mr. Romney is, by most measures, a fairly average challenger — neither a bridge-building moderate like Eisenhower, nor someone far outside of the political mainstream like George McGovern.  Meanwhile, for now, Mr. Obama has no major scandals or foreign policy debacles.  An analysis based solely on the historical patterns would suggest that Mr. Obama would be the favorite if the economy created at least 107,000 jobs a month until the election. Basically, this would represent job creation at about the rate of population growth.  But Mr. Obama is not likely to get off quite so easily. Job creation was extremely poor during his first two years in office, and mediocre during the third year, which has weighed on his approval ratings. Slightly less than 50 percent of Americans approve of his performance, polls show.  That isn’t terrible — it’s in the range where Mr. Obama might be able to eke out a victory in the Electoral College — but it’s somewhat below average.  From 1948 through 2008, the average president had an approval rating of 52 percent on Feb. 1 of the election year, according to the Roper Center archives. If Mr. Obama has an approval rating of 52 percent by November, he will almost certainly win re-election. He will also be a favorite if he is at 50 percent, because some portions of voters do not express an opinion in such polls.  The surest way for Mr. Obama to improve his approval rating will be to create jobs at a rate that exceeds the rate of population growth. Taking into account population size and his approval rating, an analysis by The Times’s FiveThirtyEight blog produces a break-even number of 151,000 jobs a month.  If we knew nothing else about the election but how many jobs were created from January to October 2012, we would deem Mr. Obama to be a favorite if the economy created more than 151,000 jobs a month and an underdog otherwise.  This is, in my view, a highly intuitive figure. When the payrolls number has come in below 150,000 jobs, economists tend to view it as bad news. A report above 150,000 jobs they regard as a hopeful sign, on balance. What’s more, current forecasts of job growth are close to that 150,000 jobs figure.  I do not mean to suggest that the jobs numbers are the only thing that will matter. If job growth averages 175,000 a month, Mr. Obama will probably be a favorite, but not a prohibitive one. If it averages 125,000 a month, he will be a modest underdog.  Still, the current forecast for labor growth points toward an extremely close election — one in which every fluctuation above or below that 150,000 threshold could matter.
With 243,000 jobs created in January, the economy is starting to look more positive. That might be a plus for the president in the November election.