"Under Republicans, recessions happen four times as frequently as under Democrats."
Hillary Rodham Clinton, Sept. 19 at the New Hampshire Democratic Party State Convention
The primary research on this question — and the source cited by the Clinton campaign when we asked — comes from a paper written by two Princeton University economists, Alan Blinder and Mark Watson.
The paper, published in July 2014, found that the economy tends to do better under Democratic presidents by numerous measures. The authors looked at quarterly economic data from 1947 through mid 2013 and the National Bureau of Economic Research's official list of recessions and found that Clinton's claim is pretty much on point.
Since 1947, there have been 11 official recessions, totaling 49 recessionary quarters. Of those 49 quarters, just eight occurred under Democratic presidents, compared to 41 under Republicans. So, over the past 65 years, quarters in recession were about five times more common under a Republican president than under a Democratic president.
"Secretary Clinton is correct in her claim," Watson, one of the paper's authors, told PolitiFact.
Looking at how many recessions started under Republicans, the difference is even more stark, noted Blinder, the co-author. Of the 11 recessions since 1947, nine under Republicans, compared to just two under Democrats.
The paper also looked further back in history to 1875 and found that the trend held, though it was less pronounced.
Economists emphasize, however, that Clinton's claim needs some additional context.
Clinton presumably wants listeners to believe that Republican policies don't work for the economy. But the research doesn't necessarily support this contention. There are far too many factors that contribute to the country's economic health.
"Democrats would no doubt like to attribute the large (Democratic/Republican) growth gap to macroeconomic policy choices, but the data do not support such a claim," the Blinder-Watson paper says.
In short, the paper found that half of the Democrats' economic advantage is a result of factors outside the control of the White House, Congress or the Federal Reserve. The other half "remains a mystery," Watson said.
"It seems we must look instead to several variables that are mostly 'good luck,' with perhaps a touch of 'good policy,' " the report says.
The authors add that Democratic presidents have benefited from higher "total factor productivity," which is essentially a measure of technological growth and dynamism. A clear example is the technology boom under Bill Clinton, which produced significant productivity gains. The authors acknowledge that it's unclear why this has been the case under Democratic presidents.
Because of all the factors at play, assigning credit for economic results is tricky, said Tara Sinclair, a George Washington University professor and chief economist for the job site Indeed.com. In fact, it's possible that causation actually runs the other way.
"It's possible that the public votes in response to economic conditions," she added, "meaning political cycles can follow economic cycles."
Clinton is right on the numbers, but her claim needs additional information to put its implication into the proper context. We rate her claim Mostly True.
Edited for print. Read the full version at PolitiFact.com.