One hundred and fifty students participated in this experiment, in groups of various sizes. A film depicting a multiple car accident was shown, followed by a questionnaire. The film lasted less than 1 min; the accident in the film lasted 4 sec. At the end of the film, the subjects received a questionnaire asking them first to describe the accident in their own words, and then to answer a series of questions about the accident. The critical question was the one that interrogated the subject about the speed of the vehicles. Fifty subjects were asked, “About how fast were the cars going when they smashed into each other?” Fifty subjects were asked, “About how fast were the cars going when they hit each other?” Fifty subjects were not interrogated about vehicular speed.
One week later, the subjects returned and without viewing the film again they answered a series of questions about the accident. The critical question here was, “Did you see any broken glass?” which the subjects answered by checking “yes” or “no.” This question was embedded in a list totalling 10 questions, and it appeared in a random position in the list.
There was no broken glass in the accident, but, since broken glass is commensurate with accidents occurring at high speed, we expected that the subjects who had been asked the smashed question might more often say “yes” to this critical question.