One way to estimate how many jobs Mr. Obama would need to create to win re-election is to look at the red regression line in the charts above. It crosses the horizontal axis at a figure of about 107,000 jobs per month.

What this means is that if we knew nothing else about the election but how many jobs were created between January and October 2012, we would deem Mr. Obama to be a favorite if the economy created more than 107,000 jobs per month and an underdog otherwise. Basically, this would represent job creation at about the rate of population growth.

However, there is no need for us to be so ignorant about some of the other evidence — and that evidence implies that Mr. Obama is not likely to get off quite so easily…

The surest way for him to improve his approval rating will be to create jobs at a rate that exceeds the rate of population growth.

We can come up with an estimate of just how many jobs this might be if we put a president’s approval rating as of Feb. 1 and the payrolls numbers into a regression equation.

I’ll spare you the math (although it is straightforward), but this works out to a break-even number of 166,000 jobs per month — not a huge number, but more than the 107,000 that we had estimated before accounting for Mr. Obama’s middling approval rating.