Illusory correlation is a psychological phenomenon where people think a connection exists between two elements when there is actually no link, or it is very minor. This plays a key role in stereotype formation, leading to a number of widely believed social attitudes. It can also create problems with activities like scientific research, where people may mistakenly identify a correlation and pursue it without realizing they are chasing a ghost. Much of this occurs on a subconscious level, making it difficult to prevent.
In a simple example of an illusory correlation, a person could decide that Asian students are better at studying on the basis of knowing several Asian students who appear to do well in school. This person might ignore evidence from students of other races who are also good at studying while also not paying attention to Asian students who don't perform as well in school. Once an illusory correlation starts to form, people tend to seek out evidence to confirm it, rather than trying to disprove it by looking for evidence to the contrary. This leads to reinforcement of the illusory correlation over time.
The formation of illusory correlations usually starts with memorable events that are easy for the person's brain to access. For instance, a student might wear her underwear backward by mistake one day and then do well on a test. This event sticks in her mind and she decides that wearing her underwear backward is lucky, even though she performed well on tests before. Readily available memories tend to rise to the top of a person's memory, and they will become evidence to support an illusory correlation even though there may be plenty of evidence that contradicts the apparent connection.
Illusory correlations can spread through society. As people hear stereotypes and urban legends, they absorb them and look for confirming information around them. Many people believe, for example, that eating sugar makes children hyperactive, although studies do not support this. When someone who believes this sees a child being active after consuming candy, it confirms the illusory correlation. Incidents where children ate candy and behaved normally afterward are not as readily available to the person's memory.
Being aware of the existence of illusory correlations is important. People who believe two things are linked can try seeking out evidence to disprove the claim to see if the correlation is real. Scientific studies sometimes provide useful information, and people may also find it helpful to do things like keeping a log. The detailed records will help people identify whether a correlation exists, and how strong it is. It is also important to be aware that correlation is not causation, and a link between two things may not be causal in nature.