The Barnum Effect: why we love astrology and personality tests

What do astrology, aura reading, fortune telling, cold reading, and some personality tests such as the MBTI have in common? They all exploit the Barnum Effect to convince people that the generated statements are personal to them. The statements are so vague, we interpret our own meaning, sometimes feeling in awe of their accuracy. “That’s so me!” you may think while reading your horoscope. Well, yes, the statement seems to align with your lived experience, because it is designed to align with anyone’s experience.

The discovery of the Barnum Effect

According to the Encyclopedia Britannica: “The Barnum Effect is the phenomenon that occurs when individuals believe that personality descriptions apply specifically to them, despite the fact that the description is actually filled with information that applies to everyone.”

The term was coined in 1956 by psychologist Paul Meehl who related the vague personality descriptions used in certain psychological tests to those given by famous showman P. T. Barnum. The effect is used when writing horoscopes or telling one’s fortune to give people the impression that the predictions are tailored specifically to them.

The Barnum Effect is also sometimes called the Forer Effect, after psychologist Bertram Forer. In 1948, he administered a fake psychology test to 39 of his psychology students. One week later, Forer gave each student a purportedly individualised results sheet, and asked each of them to rate it on how well it applied to them. The results consisted of the following list:

1. You have a great need for other people to like and admire you.
2. You have a tendency to be critical of yourself.
3. You have a great deal of unused capacity which you have not turned to your advantage.
4. While you have some personality weaknesses, you are generally able to compensate for them.
5. Your sexual adjustment has presented problems for you.
6. Disciplined and self-controlled outside, you tend to be worrisome and insecure inside.
7. At times you have serious doubts as to whether you have made the right decision or done the right thing.
8. You prefer a certain amount of change and variety and become dissatisfied when hemmed in by restrictions and limitations.
9. You pride yourself as an independent thinker and do not accept others’ statements without satisfactory proof.
10. You have found it unwise to be too frank in revealing yourself to others.
11. At times you are extroverted, affable, sociable, while at other times you are introverted, wary, reserved.
12. Some of your aspirations tend to be pretty unrealistic.
13. Security is one of your major goals in life.

Then, Forer asked his students to rate the statements in terms of how well it applied to them, on a scale of 0 for very poor accuracy to 5 for excellent accuracy. The results? Well, the students rated the personal accuracy of the statements as 4.3 out of 5 on average. That’s incredible accuracy for a psychology test.

You have probably guessed the problem: these fake results were put together by Forer by assembling various bits of copy he had found in a newsstand astrology book, and all students received the exact same list of statements, rather than a custom one as Forer had told them.

One of the most important factors when reproducing this study is to keep the statements as vague as possible, with a mix of mostly positive and some negative content. For example, using the phrase “at times” makes for a powerful Barnum Effect. See “At times you are extroverted and sociable, while at other times you are introverted and reserved” — who would not agree with that statement?

How to manage the Barnum Effect

As with most cognitive biases, half of the battle is to be aware of the Barnum Effect. However, research suggests that there are three main factors that make the Barnum Effect stronger:

• If you believe that the analysis applies only to you, and thus apply your own meaning to the statements;
• If you believe in the authority of the evaluator;
• If the analysis lists mainly positive traits.

Understanding these factors can make it easier to avoid falling prey to the Barnum Effect. First, always be wary of vague statements that may apply to anyone. When you read a statement—whether from an horoscope or a personality test—and immediately think “That’s so me!”, take a step back to wonder where it could apply to almost anyone else. If that’s the case, there is a high chance for the Barnum Effect to be at play.

It’s also good practice to question the authority of the source you are consuming. Can the author be trusted? What is their level of expertise in the domain you are currently exploring? What is their track record in offering accurate predictions? For instance, many pundits have a terrible track record when it comes to making political predictions, and some may hide behind vague statements to ensure they will never really be wrong.

Finally, pay attention to the content of the statements themselves. The Barnum Effect feeds on our need for approval by using mostly positive statements, sprinkled with a few negative ones for credibility. Go through the statements and pay close attention to the balance between positive and negative statements. If you find that particular ratio that’s a tell-tale sign of the Barnum Effect, be careful with how you may give them more weight than they deserve.

It takes practice to avoid the Barnum Effect. After all, hucksters have had centuries to hone their craft. But once you know the signs, they are easy to notice. Practice going through the Barnum Effect checklist when you read or hear something that feels strangely personal, and let your friends know they should probably not base big life decisions on their horoscope.