So what kind of thought processes contribute to belief in conspiracy theories? A study I carried out in 2002 explored a way of thinking sometimes called “major event – major cause” reasoning. Essentially, people often assume that an event with substantial, significant or wide-ranging consequences is likely to have been caused by something substantial, significant or wide-ranging.
I gave volunteers variations of a newspaper story describing an assassination attempt on a fictitious president. Those who were given the version where the president died were significantly more likely to attribute the event to a conspiracy than those who read the one where the president survived, even though all other aspects of the story were equivalent.
(Update: The “copy” is down, but you should be able to access the New Scientist. If not, here’s a sentence from the article you can Google for: “How can we account for the link between race, income level and conspiracy theories?”)