Bertram R. Forer (1914-2000) was an American psychologist who was best known for his work on the Barnum effect is well known. The Barnum effect, also known as the Forer effect, describes the phenomenon that people tend to perceive vague and general statements as being true for their own personality, even though these statements may apply to a large number of people.

In 1948, Forer conducted an influential study in which he gave his students a personality test and then presented them with supposed individual results. In reality, all students were given the same personality description, which consisted of general and vague statements. The students were asked to rate the accuracy of their individual results, and most of them thought the description was fairly to very accurate. This experiment illustrates how the Barnum effect works and how people tend to interpret general statements as specific to themselves.

Bertram Forer's work has important implications for understanding personality tests, astrology, horoscopes and other pseudoscientific practices that use general and vague statements to make people feel that the information is personal and accurate. His research on the Barnum Effect is also relevant to areas such as marketing, sales and communication, where the effect can be used to influence customers or dialogue partners.