The Barnum effect is named after P.T. Barnum, the showman who declared "therešs a sucker born every minute." He found many ways to separate "suckers", as he called gullible people, from their money.
The Barnum effect in psychology refers to the gullibility of people when reading descriptions of themselves. By personality, we mean the ways in which people are different and unique. However, it is possible to give everyone the same description and people nevertheless rate the description as very very accurate.
They way I used to run this test was to give people some personality test on paper, then give everyone an envelope with a printout of their personality, have them rate the accuracy, and then reveal to everyone that they all got the same description. So, how can it be called accurate?
Here is an example of such a Barnum description:
Whenever I ran this in class, one student would invariably raise his or her hand and declare: "Well, I was right to rate it as very very accurate because you gave everyone MY description!" And the rest of the class would laugh because they all felt the same way.
This shows how easy it is to be fooled by psychics, quack psychotherapists, fake faith healers, and others who use this technique to make people think that they really know and understand them when in fact it is just a "Spiel" or "game, played as a prank." Magicians use a method called, "The Art of Cold Reading" to give people the impression of a very accurate psychic reading. This same method is used by quack psychics and others to separate the gullible from their money.
This same Barnum demonstration has been played on introductory psychology students for over 50 years (Forer, 1949), and for some reason, it never ends up in the public conscience, thanks to the systematic misrepresentation of psychology in the popular media. It even works with personnel managers, who should know this effect by training (Stagner, 1958). It is in our textbook by Kalat, and it should be described in all other Introductory Psychology books.
You might occasionally find a TV program featuring magicians who are exposing fakes, but you will rarely see a psychologist attacking the phony "radio and TV" psychologists who listen to a person for 30 seconds and then proceed to give them a phony diagnosis followed by a public dressing down on the air. Real psychologists are horrified by this practice, but there is money to be made by radio personalities, so that game goes on and on.
Now I run the test by a computerized personality test, and even have it programmed so that the skeptical person can take the test over and over, trying different answers to see what happens. Some of my students have learned to be skeptical and check it, but an amazing number continue to rate the description as very very accurate.
There are two kinds of magicians, the honorable kind and the unethical kind. The ethical magician admits that he or she uses tricks to create illusions. The unethical magicians use the same devices to claim to have magic powers. Magicians do not reveal how tricks performed by ethical magicians are done, in order to preserve the mystery. However magicians make an exception when unethical magicians use their methods to defraud and deceive. Harry Houdini, Amazing Randi, Penn and Teller, are examples of real magicians who reveal secrets to expose phonies, quacks and frauds who claim to have psychic powers, mind over matter, or to communicate with the dead.
The moral of the Barnum Demonstration: Self-validation is no validation. Do not be fooled by a psychic, quack psychotherapist, or a phony faith healer who uses this trick on you! Be skeptical and ask for proof. Keep your money in your wallet, your wallet in your pocket, and your hand on your wallet.
Forer, B. R. (1949). The fallacy of personal validation: A classroom demonstration of gullibility. Journal of Abnormal and Social Psychology, 44, 118-123.
Stagner, R. (1958). The gullibility of personnel managers. Personnel Psychology, 11, 347-352.