As the Republican presidential contenders start to peruse poll numbers in Florida, TIME magazine’s Michael Scherer offers a different set of numbers that should boost their spirits.

For more than two decades, economist Douglas Hibbs Jr. has used a simple formula to predict the outcomes of presidential elections. He calculates the cumulative, per capita, real income growth of Americans, giving more weight to each subsequent quarter of an incumbent party’s time in the White House. With slight adjustments to account for public dislike of war casualties, his formula has worked to predict each election result since 1952, with the exception of 1996 and 2000, within 2.5 points. When he ran the numbers last October, he found that Obama was heading for a huge defeat, with a popular-vote share of 44.1%.

That number is by no means set in stone, but Hibbs estimates that income growth needs to approach 4% this year to give Obama a comfortable chance at re-election. That’s a tall order.