Only 15 percent of Americans approve of the way Congress is doing its job. But that figure could be higher by the end of the year if lawmakers use words such as "educate," "tolerate" and "cooperate" more often.

So say researchers from Canada and Germany who analyzed nearly 124 million words spoken in the U.S. House of Representatives over 18 years.

The more that elected officials used "pro-social" language, the higher the body's approval rating 29 weeks later, according to a report published in Proceedings of the National Academy of Sciences.

The reverse was true as well, the researchers found. In fact, during the 12-year stretch between 2002 and 2014, a 19 percent drop in words that conveyed a willingness to help others was followed by a 75 percent plunge in public approval.

The researchers had a hunch that the increasingly toxic rhetoric emanating from the Capitol was at least partly to blame for Congress's dismal approval ratings.

To find out whether members of Congress at least feigned concern about the needs of Americans, the researchers downloaded every transcript from January 1996 through November 2014.

After eliminating months when Congress was not in session, they were left with 123,927,807 words to analyze.

Next, they searched through all that text for 127 words and word stems that reflect notions of "collective interests and interpersonal harmony."

For each month, they calculated the proportion of words that had a prosocial meaning. Then they compared those monthly scores with monthly congressional approval ratings as measured by Gallup polls.

The result: "a striking match," the researchers wrote. The language scores and public approval figures "followed the same trajectory," with a 6.7-month lag.

But that wasn't enough to prove causation, that congressional language shaped public opinion.

Some larger force, such as the Sept. 11 attacks or a Wall Street meltdown, might be influencing them both. If so, the researchers figured it would show up in economic data or in transcripts of presidential press conferences.

So the team performed a statistical analysis that took those factors into account.

The results confirmed their hunch: "The strongest single predictor of public sentiment" toward Congress was the content of words spoken on the House floor, they found, which strengthened the case for language shaping public opinion.

Some words were more powerful than others. The researchers identified nine that seemed particularly influential: gentle, involve, educate, contribute, concerned, give, tolerate, trust and cooperate.

Although words mattered, the speakers didn't. Comments made by Democrats and Republicans were equally predictive of public approval ratings, the study found.

How do Americans know what is said under the Capitol dome? In part, it's based on news coverage that reports those words, the researchers said.

But that's only part of the answer. Somehow, congressional language is having a direct impact on the public — and it could be via C-SPAN, the researchers surmised. "Politically active viewers" of C-SPAN may influence the rest of us by spreading their impressions "contagiously within their social networks," the report's authors wrote.

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