On a list of some of the world’s best-known conspiracy theories, Americans are most likely to believe the one about JFK‘s assassination. But President George W. Bush and President Obama don't escape suspicion.

A new Rasmussen Reports national telephone survey finds that just 45% of American Adults reject as false the theory that President John F. Kennedy was assassinated by more than one shooter. Thirty-two percent (32%) believe more than one shooter was involved in the 1963 assassination in Dallas, and another 23% are undecided. (To see survey question wording, click here.)

Last November, on the 50th anniversary of the assassination, 36% of adults said Kennedy was the victim of a lone gunman, but just as many (37%) said he was the victim of a larger conspiracy.

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One-in-four adults (24%) are convinced that the U.S. government knew in advance about the September 11, 2001 terrorist attacks and did nothing to stop them, and 19% more are not sure. Only 57% say that conspiracy theory is false.

Just as many (23%) say the theory that Obama is not an American citizen is true, with another 17% who aren't sure. Sixty percent (60%) reject that theory as false.

Interestingly, however, more Americans (82%) are willing to declare as false the theory that Paul McCartney was killed in a car crash in 1966 and replaced by the Beatles than are willing to reject any of the other conspiracy theories we asked about.

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The survey of 1,000 Adults was conducted on July 16-17, 2014 by Rasmussen Reports. The margin of sampling error is +/- 3 percentage points with a 95% level of confidence. Field work for all Rasmussen Reports surveys is conducted by Pulse Opinion Research, LLC. See methodology

Twenty percent (20%) of Americans believe in the theory that a UFO carrying space aliens on board crashed near Roswell, New Mexico in 1947, and a sizable 33% more are not sure. Fewer than half (47%) reject that theory.

Past surveys show that a majority of Americans believe there is intelligent life on other planets.

How about the U.S. landing on the moon - true or false? Fourteen percent (14%) think the United States faked it, but just as many (12%) are undecided. Two years ago at the time of astronaut Neil Armstrong's death, only five percent (5%) said the moon landing was staged, and seven percent (7%) weren't sure.

A similar percentage (13%) believe Princess Diana was killed by the British Royal Family, but add another 20% who are undecided.

Americans are much less convinced of three other conspiracies on the list. Just eight percent (8%) believe in the theory that the AIDS virus was created in a laboratory by the Central Intelligence Agency, with 20% more undecided.

The same number (8%) think William Shakespeare is not the real author of the plays that are attributed to him, but when you add the 36% who aren't sure, it's clear there's sizable doubt about the authorship of "Hamlet," "Macbeth" and the others.

Only three percent (3%) think McCartney was killed and replaced by an equally talented imposter. Fifteen percent (15%) are undecided.

In general, men are more likely than women to believe most of the conspiracy theories.

Americans 40 and over are more likely than younger adults to believe JFK was assassinated by more than one shooter.

Twenty-four percent (24%) of Democrats and 29% of those not affiliated with either major political party believe the government knew about 9/11, but only 17% of Republicans agree. Roughly one-in-five adults in all three groups are undecided.

Forty-one percent (41%) of Republicans believe Obama is not an American citizen, compared to 21% of unaffiliateds and 11% of Democrats. Just over 20% of Republicans and unaffiliated adults also are not sure, but only seven percent (7%) of those in the president's party share that doubt.

Additional information from this survey and a full demographic breakdown are available to Platinum Members only.

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