Let me tell you about yourself: You pride yourself as an independent thinker and do not accept others’ statements without satisfactory proof. While you have some personality weaknesses, you are generally able to compensate for them. You have a great deal of unused capacity which you have not turned to your advantage.

Did you read the above statements and think they were eerily accurate?

Here’s the catch – they weren’t written about you.

These generic descriptions, called Barnum statements, could be about anyone regardless of their age, gender or nationality. If you were fooled, you wouldn’t be alone.

The unsuspecting millions

The phenomenon you just witnessed underlies the enduring popularity of astrology, psychics, tarot readers and faith healers – despite what scientists have to say.

Roughly 90% of surveyed people know their star sign. Most identify with the broad personality traits ‘bestowed’ by their Zodiac. For example, Sagittarians agree that they’ve been incurably bitten by the travel bug. Or, that it’s valid to excuse your stubbornness on the account of being a Taurus. Yet if you give people 12 unlabelled Zodiac personality descriptions, the probability that they correctly pick their own is no more likely than chance.

You’re so vain; you probably think this song is about you

The Barnum effect refers to the tendency to believe vague personality descriptions that are presented to be personalised, when in fact they can be almost universally applied. It is otherwise known as the Forer effect, after the American psychologist who conducted the first scientific study on the phenomenon.

In 1942, Professor Bertram R. Forer made unsuspecting first year psychology students take a personality test. (Read the original paper here.) A week later, he then gave them ‘individual’ personality descriptions comprising ambiguous statements based on their answers. When asked how accurate their description applied to them, the students gave an average rating of over 4 out of 5. In reality however, they all received an identical statement cobbled together from a news stand astrology book.

Forer and others also showed that the greater accuracy with which you rate some external description about yourself, the greater your belief in the validity of the person or system dispensing the assessment. Fifty million people in the US and UK believe that Zodiac horoscopes accurately predict their personal future.

In other words, if you truly believe you’re stubborn because you’re a Taurus, you’re also more likely to believe next month’s horoscope that you’ll hit a lucky streak in love or in your job.

What makes Barnum statements so believable?

The Barnum Effect gets its name from the winning formula used by the famous showman Phineaus Taylor Barnum: to include a “little something for everyone”. We can get sucked into believing Barnum statements because they are vague and often double-headed enough to cover all bases.

Consider the statement: “At times you are extroverted, affable, sociable, while at other times you are introverted, wary, reserved.” It seems believable because everyone’s either an extrovert or introvert, and it’s unlikely that you’ll always be one or the other all the time!

Barnum statements seduce us because they also include generally favourable statements that flatter our ego. Most people are less likely to believe them if more negative elements of their personality are described.

Other factors that can make you more susceptible is your belief in the authority of the person giving the assessment, as well as how much detail you provided.

Guarding against gullibility

Don’t like being duped?

The best defense against swindlers who use Barnum statements is a healthy dose of skepticism. Some might say being educated is enough. But even with the same level of education, those that exercised greater logical thinking skills were less prone to having the wool pulled over their eyes.

After all, what are the chances that all Taureans around the world will simultaneously get a raise next month?

Links and stuff

• Video: The Barnum Effect – Why People Believe in Astrology and Psychics
• How Are Horoscopes Still a Thing?
• Cognitive Biases – The Barnum Effect
• The science of why so many people believe in psychic powers