moonlandingNASAA photo from the actual moon landing in 1969: NASA Astronaut Buzz Aldrin looks back at Tranquility Base.

If people believe one conspiracy theory, they tend to believe more.

So if you think the Apollo 11 moon landing was faked, you might also think government officials knew 9/11 was going to happen.

Psychologists study conspiracy theories, and they're especially interested in what makes people believe in them. Back in the 1980s, they dubbed this phenomenon of believing in multiple theories the "conspiracy mentality."

Conspiracists often feel like they are part of a secret group, and find validation in finding out what they think is the "truth," psychologists have found. Today, the internet "allows theories to proliferate that in former times may not have passed the filter of mainstream media," researchers wrote recently, explaining why it's important to develop a tool "to better understand the psychological role of such beliefs in social change and individual life courses."

In a 2013 study published in Frontiers in Psychology, a team of psychologists developed a set of 15 questions to determine whether or not people are likely to subscribe to conspiracy theories.

Here are all 15 statements. If you want to score yourself, rate each as: definitely not true (1 point), probably not true (2 points), not sure/cannot decide (3 points), probably true (4 points), or definitely true (5 points). Then add up all your answers and divide by 15 to get your score.

1. The government is involved in the murder of innocent citizens and/or well-known public figures, and keeps this a secret.
2. The power held by heads of state is second to that of small unknown groups who really control world politics.
3. Secret organizations communicate with extraterrestrials, but keep this fact from the public.
4. The spread of certain viruses and/or diseases is the result of the deliberate, concealed efforts of some organization.
5. Groups of scientists manipulate, fabricate, or suppress evidence in order to deceive the public.
6. The government permits or perpetrates acts of terrorism on its own soil, disguising its involvement.
7. A small, secret group of people is responsible for making all major world decisions, such as going to war.
8. Evidence of alien contact is being concealed from the public.
9. Technology with mind-control capacities is used on people without their knowledge.
10. New and advanced technology which would harm current industry is being suppressed.
11. The government uses people as patsies to hide its involvement in criminal activity.
12. Certain significant events have been the result of the activity of a small group who secretly manipulate world events.
13. Some UFO sightings and rumors are planned or staged in order to distract the public from real alien contact.
14. Experiments involving new drugs or technologies are routinely carried out on the public without their knowledge or consent.
15. A lot of important information is deliberately concealed from the public out of self-interest.

When researchers scored a sample of about 500 people, mostly Britons and Americans (who may have skewed slightly toward conspiracy based on how they were recruited), they found an overall mean score (per item) of 2.61 (close to the "not sure" midpoint), with a standard deviation of 0.87. The test will need to be given to many people to develop a more standardized mean score for the general population, but how do you compare?

Most respondents were moderately skeptical, the researchers concluded, with the fewest believing that aliens secretly communicate with Earth (mean score: 1.88 — approaching "probably not true"), and the most believing that a lot of important information is kept from the public on purpose (mean score: 3.86 — approaching "probably true").

If you prefer a more abbreviated list, another research team published a study at around the same time with just five questions.

Respondents were able to respond saying: certainly not, extremely unlikely, very unlikely, unlikely, somewhat unlikely, undecided, somewhat likely, likely, very likely, extremely likely, or certain.

How much do you agree with these ones?

1 …many very important things happen in the world, which the public is never informed about.
2 … politicians usually do not tell us the true motives for their decisions.
3 … government agencies closely monitor all citizens.
4 … events which superficially seem to lack a connection are often the result of secret activities.
5 … there are secret organizations that greatly influence political decisions.