"Who broke Grandma's favorite vase?" As you listen to a chorus of "I don't know" and "Not me," how will you determine the culprit? Conventional wisdom says, divide and conquer, but what does scientific research show us about questioning a group of people at one time? Unfortunately, very little.
Dr. Zarah Vernham from the University of Portsmouth in the UK and her colleagues looked at 20 studies which examined deception in groups. Their review of the results was published in Frontiers in Psychology. The researchers discovered that in only one third of the studies were the participants interviewed collectively.
"Before commencing our research into the area of group deception, we were surprised at the lack of research within the area and the fact that group deceit had been primarily ignored. This was a particular concern to us because of the significant number of crimes - and investigative situations) - that involve more than one perpetrator (or interviewee)," Dr. Vernham explained.
Vernham says that in most of the studies, participants were interviewed separately. This raised concerns because how people respond in a group may be different from how they respond in when alone. She highlights that research is lacking in understanding how deception occurs in a group environment and how best to detect it.
"My interest into group deception developed as a result of my interest in collaborative memory, group dynamics and deception detection. It was though merging these three topic areas that my ideas for studying group deception developed. In particular, I am interested in collective interviewing and the novels cues to deceit that emerge from such a technique," she says.
While nothing seems more individual than memory, a group will have a collective memory of a shared event. As a group tells the story of an experience, members will interrupt each other, ask others within the group for clarification, and help each other remember. This active, dynamic process will be absent in a deceitful group which has merely memorized a script to make all their individual stories consistent.
Consistency is vital in police investigations. Unfortunately, in scientific studies, individuals who have memorized an account and prepared for an interview can have a very high degree of consistency within their own stories and between the stories of other suspects. Therefore using consistency as the main marker of truth isn't always accurate, and it must be used in tandem with other evidence.
Criminals, who are prepared with a script and prepared for an individual interview, make it more difficult for investigators to determine deceit. Standard procedures and police manuals all presume that groups of suspects will be interviewed separately in order to determine if they are telling the truth or being deceitful. Criminals also expect to be interviewed separately.
As suspects have become more sophisticated and learned means to counteract investigative tactics, we need to learn new procedures. Collective interviewing could be a valuable method of deception detection and must be more thoroughly researched.