What they found is that, relative to the overall trend, infant mortality rates were, on average, 3 percent higher during Republican presidencies, and 1 percent lower during Democratic presidencies. Though the effect is proportionally the same across races; because infant mortality rates are already more than twice as high for black citizens as white citizens, presidential party affiliation ends up affecting the black population more.

In the chart below, you can see this broken down by president (the straight line is the regression line of the overall trend). The Obama and Clinton years were the lowest, while the span of Ronald Reagan/George H.W. Bush is generally the time of highest infant mortality.

In the discussion section of the study, the researchers posit that this may be because Republicans “are more likely to view health disparities as inevitable,” and not a matter that government should intervene on, while Democrats tend to think health disparities are “a preventable social problem.”

“Although this is an oversimplified rendering of the differences in the ideological traditions, it suggests one type of reason why one might expect Republican and Democratic presidents to affect population health differently,” the study reads.

The researchers are sure to note that the correlation may be spurious—there could, of course, be other hidden factors at play. "We don't expect to find a direct causal link to one policy or one specific thing," Geronimus says. "There's nothing intentional implied."

But, she says, spurious is not the same thing as "accidental."

"While we don’t want to jump to conclusions that there’s anything directly that a Republican president or a Democratic president does that affects the infant mortality rate, I think the strength of the association, [considering] the variables we controlled for suggests that there’s a clue here," Geronimus says. "Infant mortality in the U.S. has been way too high for way too long... I think the right spirit of this paper is to generate new lines of research that maybe take slightly different directions than what's been done to date."