Barack Obama
Barack Obama has a low voiceJoshua Roberts/Reuters

Budding politicians take note: new research has found that it's not just what is delivered in your speech that's important, it's also the tone of your voice.

A new study from researchers at the University of Miami and Duke University reveals that voters tend to side with political candidates that have a deeper voice – which they associate with strength and competence. Co-author Casey Klofstad, associate professor of political science at Miami, said that this stems back to our "caveman instincts".

Klofstad: "Modern-day political leadership is more about competing ideologies than brute force. But at some earlier time in human history it probably paid off to have a literally strong leader."

The study, of which the results have been published in PLOS One, found that a deep-voiced politician is generally more successful because the tone displays greater physical strength, competence and integrity.

However, the results are not limited to just men. The outcomes, the scientists say, held up for women too. It adds that either gender with a deep voice generally have higher levels of testosterone, are stronger and more aggressive.

The team carried out two experiments; the first was to conduct a questionnaire with 800 participants, asking them about the age and sex of two hypothetical candidates and indicate who they would vote for. The candidates' ages varied from 30 to 70 but the results showed that those in their 40s and 50s were the most likely winners.

Margaret Thatcher
Margaret Thatcher famously lowered the tone of her voice to win the 1979 general electionGetty

"That's when leaders are not so young that they're too inexperienced, but not so old that their health is starting to decline or they're no longer capable of active leadership," Klofstad said. "Low and behold, it also happens to be the time in life when people's voices reach their lowest pitch."

In the second study, 400 men and 403 women were asked to listen to pairs of recorded voices saying: "I urge you to vote for me this November." However, both recordings came from the same person with the tone of their voice altered higher and lower with computer software.

The participants were then asked which voice seemed stronger, more competent and older, and who they were more likely to vote for if the candidates were pitted against each other. The deeper voiced candidates won 60 to 76% of the vote.

"We think of ourselves as rational beings, but our research shows that we also make thin impressionistic judgments based on very subtle signals that we may or may not be aware of," Klofstad said.

"But if it turns out that people with lower voices are actually poorer leaders, then it's bad that voters are cuing into this signal if it's not actually a reliable indicator of leadership ability.

"Becoming more aware of the biases influencing our behaviour at the polls may help us control them or counteract them if they're indeed leading us to make poor choices."