One of the first series of experiments to study social proof was conducted all the way back in the 1950s by Solomon Asch, a pioneer of social psychology, especially with regards to conformity.
His first conformity experiment, which went on to be widely replicated within social psychology, was conducted in 1951. In this experiment, 50 college-age participants were told that they were going to participate in a vision test. Unbeknown to the participants, they entered a room with who they assumed to be other participants, but who were actually seven confederates. Each person in the room was then shown a picture of a target line next to three lines A, B, and C, and asked which line was most similar in length to the target line. The answer was always fairly obvious, however, the seven confederates would purposefully give the wrong answer. The real participant was the last to give his/her answer, after they had heard all the other answers. Asch found that over 12 different trials, participants conformed at least once 75% of the time, showing that people will often look to others for evidence and proof of what the correct answer is.4
To further investigate this notion, Asch continued to conduct experiments throughout the 1950s, which are known usually holistically referred to as the Asch conformity experiments. While the 1951 study showed that people will use social proof for answering a question, Asch was also curious to see whether it would change the way people behaved outside of an experiment. In 1962, he conducted the “Face the Rear” experiment. In this experiment, which was a stunt conducted in collaboration with the Candid Camera show which often recorded pranks on unassuming people,5 Asch examined people’s behavior getting into elevators. Confederates were already in the elevator and faced the back (an unusual behavior). Asch found that some people followed this backwards behavior and stood in the same direction as the confederates when they entered the elevator. These people did not know that they were being watched, suggesting that even outside of the laboratory, people look for social proof to know how to behave.
However, at the time, Asch named this social and psychological phenomenon herd behavior. It wasn’t until 1984 that the term social proof became popular, when Dr. Robert Cialdini, professor of psychology, coined it in his book Influence: The Psychology of Persuasion.1 In this book, Cialdini suggested that social proof was one of six key principles of persuasion. The book is now one of the cornerstone texts of marketing and social proof has become a phenomenon widely studied to better understand how to nudge and manipulate consumerist behavior.6