Lie detection technique used by police is ‘dangerous’ and could be helping liars, study suggests

A widely-used interview technique by police to detect if a suspect is lying is not fit for use and could be helping some liars to become better at deceiving people, research has found.

Researchers led by the University of Portsmouth analysed the effectiveness of the Model Statement lie detection technique, which has been used by both the FBI and British police.

The technique is used to elicit more information from a suspect or witness by presenting them with a detailed account unrelated to the topic of the interview which is designed to act as a guide for their statement.

It is based on the assumption that longer, more detailed statements typically contain more clues to deception than shorter statements, the researchers said.

However, results from a critical analysis of the technique, published in the Journal of Investigative Psychology and Offender Profiling, have raised concerns that the method could be having a detrimental impact on attempts to bring criminals to justice.

The research team has called for an urgent review of the technique, warning it could be doing “more harm” to investigators than good.

“In my opinion it is dangerous for Model Statement to be used in practice now because there are many sources that show that while the Model Statement technique supports truth tellers to say more it also supports liars to do the same,” Cody Porter, the study’s lead researcher, said.

“The outcome is that it becomes impossible to tell the difference between someone telling the truth and someone who is lying.”

Ms Porter, who is a senior teaching fellow in psychology and offending behaviour at the University of Portsmouth, added that the technique should not be used in practice by police officers.

“As it stands, the statement can do more harm to investigations by prompting liars to produce statements that are similar in length to truth tellers, making them appear more credible or by encouraging truth tellers to provide more information that is inaccurate,” she said.

The research team also noted the diversity of Model Statement techniques currently being used and a lack of theoretical underpinning for the technique as potential problems with the practice.