Harry Potter readers in the U.S. have ?????? ???????a lower opinion of Donald Trump than the general public, and that opinion worsens as they read more books.

That's the verdict reached by a University of Pennsylvania professor in a study -- Harry Potter and the Deathly Donald -- that is set to be published in the American Political Science Association (APSA)'s Political Science and Politics journal this fall.

SEE ALSO: J.K. Rowling had the perfect response to this tweet about female orgasms

The study, which used data collection company GFK to poll a "representative sample" of 1,142 Americans, aimed to "evaluate the relevance of Harry Potter consumption" (both books and movies) to "attitudes towards Donald Trump."

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It was partially inspired, Political Science and Communication Professor Diana Mutz told Mashable, by the constant comparisons between the Republican presidential candidate and the books' villain Voldemort that began circulating in particular after the former's call to ban Muslims from the U.S.

J.K. Rowling, you'll remember, even waded into that one. "Voldemort was nowhere near as bad," she insisted in December.

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.@jk_rowling He-Who-Must-Not-Be-Named! #Voldetrump pic.twitter.com/NjFYBITwP1

— Decider (@decider) December 8, 2015

Setting out its case, the report from the Annenberg School for Communication says that few studies have examined the link between fiction and real-world opinion while non-fiction's impact has had greater scrutiny. Uncle Tom's Cabin, however, is cited as an example of a fictional book that was found in studies to change attitudes toward slavery.

The huge success of the Harry Potter franchise makes it a good subject, Mutz argues, and its oft-discussed political undertones make it an even better subject. "The sheer reach of these stories gave them the potential to have a political influence," she told Mashableover the phone Friday.

The three themes permeate the worlds of Harry and Donald.

"Despite differing perceptions of the books’ prevailing ideology," she says in the report, "there is a consensus surrounding at least three themes."

"These include 1) the value of tolerance and respect for difference; 2) opposition to violence and punitiveness; and 3) the dangers of authoritarianism. These same three themes are prominent in coverage of Donald Trump’s 2016 presidential campaign."

These themes permeate the worlds of both Harry and Donald.

For starters, mixed wizard/muggle Potter advocates for oppressed house elves and opposes Voldemort's quest for blood purity while Trump has proposed banning Muslims and ostracized even more groups of people. Non-violent conflict resolution runs through Harry Potter, meanwhile, while Trump's keen on waterboarding and has been accused of inciting violence.

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Finally, "Potter protagonists work against authoritarian characters" while "Trump portrays himself as a strongman who can bend others to his will, be they the Chinese government or terrorists.”

Original image has been replaced. Credit: Mashable

Mutz goes on to lay out three hypotheses she aims to test:

1. The more Harry Potter books read or movies seen, the greater the respondent’s acceptance of diversity and difference.

2. The more Harry Potter books read or movies seen, the less supportive respondents will be of punitive policies such as killing terrorists, torturing people suspected of terrorism, and using the death penalty.

3. The more Harry Potter books read or movies seen, the less supportive Americans will be of Donald Trump.

Mutz polled 1,142 Americans in 2014 and 2016. She asked them about their Harry Potterconsumption, their attitudes toward everything from waterboarding to the death penalty, the treatment of Muslims and gay people and in 2016 their feelings about the Donald.

They had to answer on a zero to 100 scale.

Each Harry Potterbook read lowered respondents' evaluations of Donald Trump by roughly two to three points.

Mutz told Mashableshe was "surprised by the strength of the results," particularly because "after taking so many different factors into account, the relationship was still quite significant."

The majority of Trump's supporters are white men over 50, according to a July Pew Research Center poll. Credit: Jeff Siner/Charlotte Observer/TNS via Getty Images

Mutz also collected data based on viewership of the movies, but found these didn't predict opposition to Trump.

"Reading inherently requires much higher levels of attention and allows for greater nuance in characters, many of whom are neither wholly good nor wholly bad," the report's press release says. "Due to length, movies must leave out material from the full books, and they are more likely to emphasize action over the characters’ internal dilemmas and introspection."

Interestingly, the study also found that Democrats, Republicans and Independents have all read Rowling's books in roughly equal numbers.

A note of caution

The study has been peer reviewed ahead of its full publication this fall but the headline findings come with caveats. As Mutz admits to Mashable, "most studies on [the impact of] fictional stories on political views have been done in controlled labs. You can be absolutely certain what’s causing them."

"Observational data have inevitable weaknesses for causal inference," she adds in the report itself.

Mutz points to the "widespread exposure" of the series, its years-long release schedule and subsequent dominance of bestseller lists, and says that that gives it a chance to have a systematic and cumulative impact. While researchers might study the impact of a single episode of Law & Order, say, Harry Potter's potential influence is far more pervasive.

Her figures, she says, "have the clear advantage of being able to document influence that has occurred in the real world, not by the forced exposure of a small number of experimental subjects to a story they would not otherwise encounter."

Any potential misgivings aside, one author in particular was pretty pleased with the outcome Friday...

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Mashablehas reached out to the Trump campaign for comment.