The Barnum Effect was first clearly demonstrated in a famous psychology experiment by Bertram Forer in 1948.

In 1948, psychologist Bertram Forer gave his students a personality test. A week later, he handed back what each student believed was a personalized analysis of their character. He asked them to rate its accuracy on a scale of 0 (very poor) to 5 (excellent). The average rating was a surprisingly high 4.26. What the students didn't know was that every single one of them received the *exact same* personality description, pieced together from horoscope clippings. This showed how easily people accept vague, general statements as specifically true about themselves.