Bertram Forer gave his introductory psychology students at Los Angeles City College a personality test, collected it, and returned individually typed profiles a week later. He asked each student to rate, on a scale of zero to five, how well the profile described them personally. The average was 4.26. Almost everyone rated it four or better.
Every student had received the identical text. Forer had assembled it from a newsstand astrology book.
The passage runs, in part: You have a great need for other people to like and admire you. You have a tendency to be critical of yourself. You have a great deal of unused capacity which you have not turned to your advantage. While you have some personality weaknesses, you are generally able to compensate for them. Disciplined and self-controlled outside, you tend to be worrisome and insecure inside.
Read it again and notice the construction, because the construction is the technique. Almost every sentence is double-headed, asserting a trait and its opposite in a way that lets the reader select whichever fits. Almost every one is socially desirable, so accepting it is pleasant. All of them are vague enough that the reader has to supply the content — the specific memory of a time they were self-critical, the particular unused capacity they have in mind. And once the reader supplies the content, the profile is describing something they actually recognize, because they wrote it.
Forer called this the fallacy of personal validation; it is now usually called the Barnum effect, after the showman's remark about having something for everybody. The mechanism is subjective validation combined with confirmation bias: confirming instances are generated by the reader and disconfirming ones are not searched for.
Subsequent work found the amplifiers, and they are worth knowing because they tell you what a cold reader is doing. Acceptance rises when the profile is believed to be uniquely tailored to the individual, which is why the ritual of collecting information first matters even when the information is not used. It rises when the assessor is perceived as an authority. It rises when the statements are favorable — negative Barnum statements are accepted much less readily. And it rises when the subject has invested effort or money in obtaining the reading, which is chapter 13 arriving from an unexpected direction.
The industries are obvious once the mechanism is visible: astrology, cold reading, mediumship, graphology, many commercial personality instruments, and a large amount of what is sold as psychometric assessment to human resources departments. Some of these are frauds, and some are sincere practitioners who have themselves been convinced by the same effect, since the client's evident recognition is powerful feedback.
The test that separates a real assessment from a Barnum reading takes one question, and it is the falsifiability test. What would this profile have said about someone unlike me? A description with real information content excludes something. It says you are impatient with detail, which means it would have said the opposite of someone else, and you would have noticed if it were wrong. A Barnum profile excludes nobody, which is why it feels so accurate and why the accuracy is worthless.
If you cannot state what the reading would have looked like if it were false, it has not told you anything about yourself.
Defense: The Recruiter’s Tells: Cult Red Flags in the First Ninety Days