Fascinating New Scientist article (for subscribers only, but there’s a copy here) on conspiracy theories, and why we believe them:

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.

To appreciate why this form of reasoning is seductive, consider the alternative: major events having minor or mundane causes — for example, the assassination of a president by a single, possibly mentally unstable, gunman, or the death of a princess because of a drunk driver. This presents us with a rather chaotic and unpredictable relationship between cause and effect. Instability makes most of us uncomfortable; we prefer to imagine we live in a predictable, safe world, so in a strange way, some conspiracy theories offer us accounts of events that allow us to retain a sense of safety and predictability.

Other research has examined how the way we search for and evaluate evidence affects our belief systems. Numerous studies have shown that in general, people give greater attention to information that fits with their existing beliefs, a tendency called “confirmation bias.” Reasoning about conspiracy theories follows this pattern, as shown by research I carried out with Marco Cinnirella at the Royal Holloway University of London, which we presented at the British Psychological Society conference in 2005.

The study, which again involved giving volunteers fictional accounts of an assassination attempt, showed that conspiracy believers found new information to be more plausible if it was consistent with their beliefs. Moreover, believers considered that ambiguous or neutral information fitted better with the conspiracy explanation, while non-believers felt it fitted better with the non-conspiracy account. The same piece of evidence can be used by different people to support very different accounts of events.

This fits with the observation that conspiracy theories often mutate over time in light of new or contradicting evidence. So, for instance, if some new information appears to undermine a conspiracy theory, either the plot is changed to make it consistent with the new information, or the theorists question the legitimacy of the new information. Theorists often argue that those who present such information are themselves embroiled in the conspiracy. In fact, because of my research, I have been accused of being secretly in the pay of various western intelligence services (I promise, I haven’t seen a penny).