If Donald Trump makes you want to say "Expelliarmus!" you're not alone.

A new study found an intriguing correlation between how many "Harry Potter" books a person read and his or her opinion of the Republican presidential candidate: The more books, the less they liked Donald Trump.

Titled "Harry Potter and the Dangerous Donald," the study — authored by University of Pennsylvania professor Diana Mutz — polled 1,142 Americans, asking how many Potter books they'd read and their feelings about Trump, whom they were asked to rate on a scale of zero to 100.

With each book completed, a person's opinion of Trump dropped on average by about two to three points, Mutz found.

"This may seem small," she told science news site Phys.org. "But for someone who has read all seven books, the total impact could lower their estimation of Trump by 18 points out of 100. The size of this effect is on par with the impact of party identification on attitudes toward gays and Muslims."

"The anti-Trump theme in that they don't use curses and aggression unless they have to," Mutz said in a call with ATTN:. "And [it's] very much the opposite of Voldemort and the kind of trips that he's on and his desire to dominate others and to categorize people as pure and impure, Muggles and non-Muggles."

"It may simply be too difficult for 'Harry Potter' readers to ignore the similarities between Trump and the power-hungry Voldemort," Mutz said.

Mutz discovered that the correlation held even if a person identified as politically conservative.

"[Voldemort] cares a lot about blood purity and about whether you're a pure wizard or a 'mudblood' and so on and so forth, and everybody who isn't a pureblood is constantly afraid for their lives," Mutz told ATTN:. "And certainly Trump's statements about the treatment of Muslims, and as well as things like family members in Paris, all suggest this kind of emphasis on certain groups being good and others evil and certainly the racial kind of animosity that has come out of this campaign."

Mutz found that subjects' party identification did not make them more or less likely to have read the books.

"I was thinking that religious conservatives might dislike the wizard-magic kind of theme, but, actually, Republicans, Democrats, conservatives were all equally likely to expose themselves to the books," Mutz told ATTN:.

Reading even a single "Harry Potter" book had a huge effect.

Mutz looked into whether the correlation could have resulted from self-selection: People might have observed the first book's social and political messages and stopped reading if they didn't agree with them. But she found that even if a person read only one "Harry Potter" book — any book — he or she was likely to view Muslims and gay people five to six points more positively and to view Trump nine points more negatively, the study found.

"Quitting the series after one book therefore becomes irrelevant in [light of] these results" showing a strong effect of reading a single book, Mutz said.

(Mutz included the "Harry Potter" movies in her study and concluded that there wasn't a significant correlation between watching them and political opinions.)

The books also correlated with people's feeling positively about Muslims and LGBT people.

One of the central themes of the "Harry Potter" series is tolerance, Mutz said.

"The messages are tolerance for creatures as well as humans who aren't like you, and we see that throughout in terms of Hermione and the society for Protection of Elfish Welfare and Dobby and the fact that they are friends with Hagrid the Giant," Mutz said. "They don't treat him or stigmatize him in a negative way."

"Things aren't what they seem on the surface," Mutz added. "I think that kind of mutual respect that Harry demonstrates, even in the very last book where his son says, 'Oh, I hope I am not in Slytherin,' Harry says, 'You know, one of the greatest men I ever knew was a Slytherin.' The idea is not to categorize people, not to dismiss their value."