January 27th, 2014

Discontinue the use of polygraph on assault victims

By Sumedha Jalote, Communications Executive, Association of Women for Action and Research

We read with interest of psychologist Professor Aldert Vrij’s visit to Singapore and his statement that law enforcement agencies often rely too much on mechanical methods of lie detection (“Busting the myths of lie detection”, Jan 19).

police1AWARE’s Sexual Assault Befrienders Service (SABS) has encountered numerous cases where those filing complaints of sexual assault or rape are required to take a polygraph lie detector test while making a police report.

Given international expert consensus on the poor accuracy and reliability of these tests, we question whether this practice should continue.

In 2004, the British Psychological Society found that “[Even] in the most favourable circumstances polygraphic lie detection accuracy is not high”. In 2003, the United States National Research Council (NRC) concluded that the reliability of the polygraph is questionable, and neither technological nor methodological advancement was likely to improve that reliability.

A polygraph does not directly detect deception. Instead, it measures physiological responses such as blood pressure and pulse rate believed to result from psychological states accompanying deception. These responses, however, can be caused by many other factors, such as embarrassment, outrage or distress.

Administering the polygraph to rape and sexual assault complainants inevitably involves questioning them about highly sensitive and potentially distressing matters, which are likely to elicit emotional responses.  This raises the possibility that the polygraph results become especially inaccurate in this context.

A substantial number of our SABS clients have indicated that undergoing a polygraph caused them anxiety. This can worsen the traumatic effects of sexual assault.

Due to these concerns, many jurisdictions have discontinued the use of polygraph testing on rape and sexual assault complainants.

Polygraph results are not admissible in court in Singapore, and the process and reasons for administering this test are not generally made clear to the victims.  It is unfair that decisions about how to handle a sexual assault complaint should be made on the basis of such an unreliable practice.

Many victims of sexual crimes do not make police reports because they fear being disbelieved. Forcing victims to take a lie detector test reinforces their fear of not being believed, and is of dubious value to the investigation.  We recommend that the practice be discontinued.

An edited version of this letter was published in the Straits Times Forum on 26 January.


  1. Sureesh

    Hard to believe that the police in singapore could do such a silly thing.

    I wonder even with having scholars in top positions in the force, how could the police be so ignorant.

    That just goes to show that having scholars is not a panacea.

  2. Emily

    I agree, there is every reason to stop the practice of using polygraph tests. It isn’t reliable, and only serves to unfairly punish survivors of sexual assault.

  3. […] national “crime-prevention” adverts that blame the victim, to the use of polygraph (lie detector) tests on sexual assault victims, to Members of Parliament trivializing rape on Facebook, to the lack of recognition of marital […]