Witnesses correct each other's errors. Two recently published research studies by legal psychologists Annelies Vredeveldt and Peter van Koppen at Vrije Universiteit Amsterdam show that witnesses make fewer errors when they are interviewed together than when they are interviewed separately. This stands in sharp contrast with current police guidelines to always interview witnesses separately.
In a unique collaboration between VU Amsterdam and the Toneelschuur theatre in Haarlem, in the first study the researchers asked attendees of an emotional play to testify about a rape-and-murder scene they saw a week earlier. Witnesses were interviewed either in pairs or alone. Two witnesses who were interviewed together reported the same amount of information but made substantially fewer errors than two witnesses interviewed separately. In the second study, the researchers interviewed a larger number of witnesses (80 people) and found the same result.
These findings are surprising in light of previous legal psychological research showing that witnesses can contaminate each other's memory. The difference is that in those studies, artificial ways were used to increase errors, such as letting the witness talk to a 'fake witness' who purposefully introduced errors in the discussion. In contrast, the research by VU Amsterdam investigated naturalistic discussions between witnesses.
Eyewitness pairs with more effective communication styles remembered more
Moreover, the research showed that couples with an effective communication style remembered more together than couples who communicated less effectively. The research shows that the best way of collaborating is to repeat or rephrase your partner's statements and then elaborate by adding extra information.
"The research findings show that collaboration between witnesses can also have benefits," the researchers said. "Until now, most people assumed that discussion between witnesses has only disadvantages." Vredeveldt and Van Koppen expect that this research will lead to widespread interest from both academics and police practitioners.
The research has been published in two international academic journals: the first study in Memory and the second study in Legal and Criminological Psychology. The studies form part of the research conducted by the Amsterdam Laboratory of Legal Psychology (ALLP).
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