A wide-ranging new analysis of congressional-floor speeches finds that political polarization has "exploded" over the past 20 years, and is now "far greater today than at any point in the past."

The study, by economists at Stanford and Brown universities and the University of Chicago, analyzed the entirety of the congressional record going back to 1873. The researchers built a sophisticated model capable of measuring how easy it would be for a typical listener to guess a speaker's political party based on the words the speaker used in one minute of speech.

The results were striking: from the 1870s until roughly 1990, "partisanship was low and roughly constant," according to the analysis of congressional language. In most years during that time period, a listener would have a little more than a 50 percent chance of "correctly guessing a speaker's party based on a one-minute speech."

But in recent years political language has changed dramatically. "Beginning with the congressional election of 1994, partisanship turned sharply upward, with the probability of guessing correctly based on a one-minute speech climbing to 83 percent by the 110th session (2007-09)."

To conduct the analysis, the researchers looked for "partisan phrases" — phrases whose removal from a speech would make it harder to infer a speaker's political leanings. Those phrases have changed greatly over time.

In the late 1800s, hot-button phrases were related to discussions of tariffs and protectionism, such as "tariff tax," "increase duties" or "fisheries treaty." These were phrases that showed up in party platforms relating to the big political debates of the day.

By the late 1960s, Democrats were aggressively trying to expand the federal safety net. Phrases like "food stamps" and "school lunch" carried highly partisan connotations. And by the mid-2000s, the partisan contours of our present-day political fights come into focus. Phrases like "illegal immigrant" and "higher taxes" become associated with Republican partisanship, while Democrats begin leaning on terminology related to drawing down the wars in Iraq and Afghanistan.

According to the study, the rise in partisanship is not only about changes in political topics. The parties have always fought over things like taxation, immigration and the proper role of government. It's due, rather, to the choice of language that partisans use to frame the debates — changing "estate tax" to "death tax," for instance, or subtly morphing "global warming" to "climate change."

The introduction of these novel and ideologically skewed methods of framing debates starts right around the mid-1990s, leading to the abrupt and dramatic rise in partisanship since then. According to the economists' analysis, that's no accident, and it can all be traced primarily back to one seismic event: the Republican takeover of Congress in 1994, and the rise of House Speaker Newt Gingrich and his "Contract with America."

That year, Republicans took control of the House for the first time in 40 years. "This election is widely considered a watershed moment in political marketing, as consultants such as Frank Luntz applied novel focus-group technologies to identify effective language and disseminate it broadly to candidates," the economists write. You may recall Luntz as the man credited with identifying the persuasive power of some of the terms mentioned above, like "death tax" and "climate change."

To test their theory on the primacy of the Gingrich Revolution, the economists extracted all the phrases used in the famous Luntz-tested, Luntz-approved "Contract with America" and ran the same analysis on them alone. This chart from their paper shows that the use of these phrases spiked in 1994 and has remained historically high since, and that they tend to be highly partisan in use.

This new analysis has some important similarities and differences with other measures of polarization. The most well-known partisanship metric is based on lawmakers' votes, not on their speech. That measure also shows partisanship rising sharply in the modern era.

But the vote-based measure shows the increase starting in about the 1970s, rather than the mid-1990s. And it also shows a high degree of polarization back in the late 1800s. This has led many political scientists to argue that our current divided politics aren't necessarily an anomaly, but rather a return to a historic norm after a period of relative partisan unity.

But the economists' analysis of political language tells a very different story, one in which the current state of partisan warfare is unprecedented. You can see how the two measures differ in the following chart from the economists' paper.

These two analyses aren't necessarily contradictory. "Speech and roll-call votes should not be seen as two different manifestations of a single underlying ideological dimension," the economists write. "Rather, speech appears to respond to a distinct set of incentives and constraints."

It may boil down to a difference between action and speech. Politicians today may be voting along partisan lines similar to how lawmakers worked in the late 1800s. But today's political rhetoric — the ways lawmakers frame their arguments and try to portray the arguments of the opposing side — may be more radically divided than they've been at any point in the historic record.

In other words, "Democrats and Republicans now speak different languages to a far greater degree than ever before," the study concludes. If it seems like today's politicians are talking past one another, rather than to one another, it may be because that's exactly what they're doing.