Cognitive Biases — The Barnum Effect

Michael Gearon
4 min readAug 26, 2018
Bertram R. Forer “The Fallacy of Personal Validation: A Classroom Demonstration of Gullibility”

The Barnum Effect in psychology, also known as The Forer Effect, is when an individual believes that personality descriptions apply specifically to them, for example, reading your horoscope in a newspaper and realising it’s surprisingly accurate. We all know that horoscopes are written for the masses, but we can’t help feel but it’s meant for us. Let’s rewind the clock and examine where the Barnum effect came from and how it’s being used today with great effect on websites and mobile apps.

Why is it called The Barnum Effect?

P.T. Barnum

It comes from the 19th century American P.T. Barnum (you probably know who he is from The Greatest Showman film). He said that a “sucker is born every minute” - people are gullible and want to believe what they’re told, so they’ll think general sweeping statements are solely about themselves. We’ve seen this trick being used for years with psychics, magicians, palm readers, horoscopes and now on digital media platforms.

More officially, this cognitive bias stems from Professor Bertram R. Forer born in 1914, who was an American psychologist and was best known for the Forer Effect. You can read the original paper online: “The Fallacy of Personal Validation: A Classroom Demonstration of Gullibility”.

The original experiment was conducted in 1948 on his students where he handed them a personality test. He claimed that each survey would be analysed and then given back to them with an individual personality assessment. Rather than assessing each test and giving individual feedback instead he just gave back a paragraph full of generalised statements like “you have a great need for other people to like and admire you,” “you have found it unwise to be too frank in revealing yourself to others” and “you have a tendency to be critical of yourself”.

What topped this test off was, afterwards, the students were asked to evaluate their personality feedback, rating it between zero and five, with five being the most accurate and zero being the least. The average rating was 4.26. To this day this experiment continues and holds an impressive ‘accuracy’ record.

How is this applied to websites?

Now we know how the Barnum Effect works let’s look for examples of how it’s used on a day-to-day basis:

Facebook “personality quizzes”

Facebook personality quizzes

Probably one of the best examples of the Barnum Effect is the Facebook personality quizzes that you see on every other post. Looking at the above example it says:

Rachael is loyal to the people that are loyal to her. Rachael values loyalty. Be like Rachael

Using a first name to tailor the content and then adding some wide-reaching trait makes a general statement seem more personal - most people do value loyalty (or would like to think they do), so it resonates with the majority. The reality is that Susan, Tracey, Bob and Dave all probably had these same messages but with their own name instead.

Spotify’s “handpicked” music


On a daily basis, Spotify pulls together “your daily mix” which they claim is “packed with your favourites”. Although all of this is automated, it makes you feel that Spotify has created these custom handpicked playlists just for you.

Netflix email newsletter


Netflix regularly emails me with movie suggestions and a section which they feel showcases films relevant for me - “top films for you” - again, it feels like Netflix has gone that extra step to understand my needs but this is all automated. There are 1000s of other people that are sent pretty much the same email with slightly different film suggestions.

Closing thoughts

Before researching the Forer Effect in detail, I understood this technique of cognitive bias but didn’t appreciate how long it’s been used for, and how it’s been adapted over the years. This technique is particularly powerful in the modern day, as companies become smarter with customer data and can easily create content that feels tailored for you, but instead it’s just a generic frame which is then filled with your data.

Thanks for reading! If you enjoyed this article and want to see more you can follow me for more articles — Mike



Michael Gearon

Senior Interaction Designer and Co-Author to Tiny CSS Projects