Research suggests that Donald Trump’s bombastic communication style was the key to his success during the 2016 Republican primary.

The study found that Trump employed speech patterns that are often associated with narcissism.

“My psychology lab has focused on the dark side of personality for 20 years. We concluded that four dimensions stood out in the empirical literature: psychopathy, Machiavellianism, sadism, and narcissism,” explained study author Delroy L. Paulhus, a professor at the University of British Columbia.

Previous research has indicated that U.S. presidents with personality traits associated with grandiose narcissism are rated as better leaders and are more persuasive.

“During his 2016 campaign to become the Republican nominee, it became clear to all that Donald Trump is the prototypical narcissist,” Paulhus said. “With many speeches now publicly available, we sought to code his narcissism using objective methods. New computer software is now capable of generating a wealth of such indicators.”

The researchers analyzed early campaign speeches of the top nine Republican presidential candidates: Donald Trump, Ted Cruz, John Kasich, Ben Carson, Jeb Bush, Marco Rubio, Rick Perry, Lindsey Graham and Mike Huckabee. They also examined how the GOP candidates used Twitter.

Paulhus and his colleagues found that Trump’s language contained substantially more grandiosity and substantially less formality than the rest of the candidates. Both grandiosity and informality, meanwhile, were associated with political success in the GOP primary race.

Trump also ranked highest on the use of first person pronouns, had greater vocal dynamics, and used Twitter more often.

The findings were published in Personality and Individual Differences.

“Bottom line is that a politician’s vocal style is at least as important as the content of his speeches,” Paulhus told PsyPost. “In debating with 17 other candidates, his political platform differed little from the others. ”

“However, his statements were typically more extremely and bombastically worded,” he explained. “The software analyses also singled out a dynamic vocal range, and a strong preference for simple, informal wording. All of these variables predicted the number of states won in the Republican primaries.”

“We did not analyze the federal election, where Trump debated with Hillary Clinton. Many more variables played a role at that stage. And speech content certainly played a role.”

The study, “Explaining Trump via Communication Style: Grandiosity, Informality, and Dynamism” was also co-authored by Sara Ahmadian and Sara Azarshahi.