GOP nominee Donald Trump has had a strange past few months, to say the least, prompting some to question his mental fitness.

Research psychologist Kevin Dutton of the University of Oxford set out to figure out just how prone to psychopathy Trump is. Dutton also analyzed the psychopathy of former world leaders.

What he found, as detailed in a piece he wrote for Scientific American, is that Trump is more of a psychopath than Adolf Hitler.

"In an ongoing study, I had been asking the official biographers of prominent historical figures to fill out, on their subject's behalf, an abbreviated version of the Psychopathic Personality Inventory–Revised," Dutton explained. "This short psychometric test uses 56 questions to quantify a person's psychopathic personality traits."

Dutton commissioned an unnamed BBC political news anchor to fill out the test on behalf of the four leading contenders in the presidential primaries, according to the New York Daily News. For the deceased leaders, historians were asked to do the same.

Using this metric, Dutton found that Trump scored a 171 to Hitler's 169. Saddam Hussein was rated most psychopathic with a 189, and Mahatma Gandhi the least, with 119. Democratic presidential nominee Hillary Clinton scored a 152, Ted Cruz scored a 156, and Bernie Sanders scored a 129.