The Forer effect is the seeing of a personality statement as "valid even though it could apply to anyone", and is named after the psychologist who famously demonstrated it1. In 1949, Bertram Forer conducted a personality test, and then gave all of his students exactly the same personality profile, which he constructed from random horoscopes. The students rated the accuracy of their profile at over 80% on average2! This was occasionally previously known as the Barnum effect after a popularist entertainer. Extensive studies have found that this effect applies well to horoscopes, other astrological readings, messages given from the dead by spiritualists, various cold reading tricks and other profiling endeavours3. It is often mistaken for being a product of magical or supernatural means.
“In 1948 psychologist Bertram R. Forer (1949) gave his students an apparent personality test and later distributed the resulting personality profiles. Students were quite impressed with the results, giving the test as average accuracy rating of 4.26 (0='very poor,' 5='excellent'). Of course, all profiles were exactly the same: a generic reading pasted together from random horoscopes. The 'Forer' test is now a classic, [demonstrated] in hundreds of classrooms each year.”
“The Barnum effect refers to the tendency for people to accept as uncannily descriptive of themselves the same generally worded assessment, as long as they believe it was written specifically for them on the basis of some 'diagnostic' instrument such as a horoscope or personality inventory.”
"How We Know What Isn't So: The Fallibility of Human Reason in Everyday Life" by Thomas Gilovich (1991)1
“The Forer effect refers to the tendency of people to rate sets of statements as highly accurate for them personally even though the statements could apply to many people. [...] Numerous studies involving personality assessments, astrological readings, biorhythm charts, and validation of messages from the dead that have come through alleged mediums have found that almost regardless of what data you present subjects with, they rate the accuracy at about 80%.”
"Unnatural Acts: Critical Thinking, Skepticism, and Science Exposed!" by Robert Todd Carroll (2011)3