Political ideology in the study was defined by the speaker’s voting record or party affiliation.

The study also examined publicly available photographs of 533 members of Congress, finding that conservative politicians were less likely than liberals to display smiles involving facial muscles around the eyes, a measure that previous research has found to be associated with genuine emotion.

Two other studies analyzed the emotional tenor of language in 47,000 Twitter posts by nearly 4,000 Twitter users and the photographs of 457 users of LinkedIn, with similar results. The Twitter users were identified as liberal or conservative depending on whether they subscribed to feeds from the Democratic or Republican parties. The LinkedIn users were affiliated with organizations associated with liberal or conservative ideologies, like Planned Parenthood and the Family Research Council.