Polygraph:a lie-detector test
a machine designed to detect and record changes in physiological characteristics, such as a person's pulse and breathing rates, used especially as a lie detector.
Published on: Mar 4, 2016
Transcripts - Polygraph:a lie-detector test
• Is scientific, diagnostic, instrument known as
• Appropriate to be called as truth verifier.
• Invented in 1921 AD by John Augustus Larson.
• Measures several physiological indices.
• Used by FBI and CIAA (US law enforcement
and federal government agencies).
How can a machine detects whether someone
is telling truth or not ?
• At first pre-test than diagnostic question is
• 3 basic type of question:- 1) irrelevant 2)
relevant 3) control
• Passed if psychological response to diagnostic
question is larger than those during relevant
• Very accurate however it is unreliable.
• According to APA (American polygraph
Associatiation) in 250 studies over 25 years.
Accuracy of polygraph is 90- 95%.
• Lie detector test cost 500 pound in UK and
400$ in USA.
How there recording made?
Two strain gauze is taken. One across chest
and another across abdomen.
Ability of skin conductivity is recorded by
placing electrodes pads on finger.
Cardio- vascular activity is recorded using
standard blood pressure cuff placed on
Who should not take polygraph
Person with serious heart
Nerve damage or paralysis.
Any person who has stroke or is an
epileptic (person who is in pain,
For polygraph test
o Good night sleep.
o Don't consume alcoholic beverage.
o Don't use illegal drugs for 24 hrs prior to
o Injury , illness or physical condition that can
Issues that a Polygraph test is done
• Criminal Investigation
• Sex Offenders
• Child Custody
• Personal Investigation
How to pass Polygraph Test?
• Remember that polygrapher is not your friend:-
• Beware of pre-test tricks:-
• Conceal your knowledge of polygraph:-
• Don't believe in rumour:-
• Answer firmly, seriously and without hesitation:-
• Biting tongue is highly affective:-
• Change breathing pattern when control question
• Handle the post test interview:-
In Context Of
Confession of truth using such method is the severe
violation of human right .
Confession are obtained using 3rd degree interrogation
methods like merciless beating, deprivation of water and
food, questioning in dark room etc.
So nepal police alternative to 3rd degree treatment is
Result Of Polygraph In Nepal
• Upto now 12-13 incident has been investigated by
polygraph in Nepal.
• Mahendranagar :-Unidentified mask people looted 2
crore 31 lakhs
• Ramananda chowk of Janakpur : Bomb blast incident by
Sanjay saha (CA Member) arrested by taking 2 hour
• Dhangadi: Nepal police used polygraph for carrying out
investigation into incident of looting about 4 crore of
Nabil bank by its own empolyee.
Conclusion And Discussion
Polygraph lacks constitutional and scientific validity.
India supreme court has also banned to use polygraph
citing it is a violation of human right to life and privacy.
Even in USA , land where polygraph is invented ,
Polygraphy has been banned by supreme court treating
it as unreliable.
But in nepal nobody has been raising such question so it
is in practice.
• http://cib.nepalpolice.gov.np/ accessed on
• http://www.webmd.com/ accessed on
accessed on 15/03/2014