Bertram Forer

Bertram Forer was born in Springfield, Massachusetts, in 1914 and trained in clinical psychology at UCLA after undergraduate study at the University of Massachusetts, and after wartime service as a psychologist in a military hospital in France he settled into a career split between a Veterans Administration mental health clinic in Los Angeles and private practice in Malibu. In 1948 he ran a personality assessment exercise with his introductory psychology students that has since become one of the most repeated demonstrations in the history of the discipline: he administered a diagnostic interest inventory to the class, told each student the resulting personality sketch had been prepared individually from their own answers, and asked them to rate its accuracy on a scale of zero to five.

Every student received the exact same sketch, a paragraph Forer had copied almost verbatim from a newsstand astrology column, vague and flattering enough to read as true of nearly anyone: statements about needing others' approval while remaining independently minded, having unused capacity that had not been turned to advantage, and disciplined self-control masking inner worry. The average rating his students gave the sketch for personal accuracy was 4.26 out of 5, a result Forer published the following year and that has been replicated with almost identical average scores by researchers repeating the demonstration for more than seven decades since.

What Forer's demonstration exposed became known as the Forer effect, or, drawing the same point from an older showman's reputation for having something for everyone, the Barnum effect: people readily accept a vague, generally flattering personality description as a specific, personally accurate reading of themselves, especially when told an authority has prepared it just for them, and especially when the description leaves room for the reader to supply their own confirming details. The effect does not depend on the description coming from astrology specifically, though Forer's own sketch did; cold readers, personality tests, tarot readers, graphologists and generic corporate feedback forms all trade, knowingly or not, on the same mechanism.

Because the effect predicts that almost any vague positive description will feel personally true regardless of its actual source, it has become the standard skeptical tool for explaining why divinatory and pseudo-diagnostic systems report such high satisfaction from their clients without that satisfaction constituting evidence the system itself works. Psychologists studying astrology, tarot and personality profiling routinely cite Forer's 1948 demonstration, still the most replicated single experiment in the psychology of belief, as the baseline any claim of a system's real predictive accuracy has to be measured against and rule out before it can be taken as more than an artifact of how readily people accept flattering vagueness as insight.