How a lie detector works

President Uhuru Kenyatta on Friday, June 1 ordered all procurement and accounting heads in government to undergo lie detector tests in fresh vetting as the State intensifies war on graft.

Speaking during the 55th Madaraka Day celebrations at Kinoru stadium in Meru, President Kenyatta ordered that the government officials undertake the tests within the next 30 days; and that those who will fail the vetting will face the sack.

“All heads of procurement and accounts in government ministries, departments, agencies and parastatals will undergo fresh vetting including polygraph testing to determine their integrity and suitability,” said the Head of State.

But, just how does a lie detector work?

Citizen Digital explores the workings of this invention, which is mostly used in police investigations, and in extreme cases, job application process.

In the U.S., for instance, certain government jobs with the FBI or CIA require polygraph tests.

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The goal of a lie detector is to see if the person is telling the truth or lying when answering certain questions.

When a person takes a polygraph test, four to six sensors are attached to him, this, according to

A polygraph is a machine in which the multiple (“poly”) signals from the sensors are recorded on a single strip of moving paper (“graph”). The sensors usually record: a person’s breathing rate, pulse rate, blood pressure and perspiration.

Sometimes a polygraph will also record things like arm and leg movement.

When the polygraph test starts, the person mandated to pose questions asks three or four soft ball questions to establish the norms for the person’s signals like name, sex and age.

Then the real questions being tested by the polygraph are asked. Throughout questioning, all of the person’s signals are recorded on the moving paper.

Both during and after the test, a polygraph examiner can look at the graphs and can see whether the vital signs changed significantly on any of the questions. In general, a significant change (such as a faster heart rate, higher blood pressure, increased perspiration) indicates that the person is not telling the truth.

When a well-trained examiner uses a polygraph, he or she can detect lying with high accuracy, says

However, because the examiner’s interpretation is subjective and because different people react differently to lying, a polygraph test is not perfect and can be fooled.

New reports have since been published providing guidelines on how to cheat in a lie-detection test.

President Kenyatta, who has been blamed for what his critics have said is his laxity in fighting corruption, said government’s efforts in combating graft will be sustained.

“In the coming days, you will hear of other tougher actions that will be taken by my government. We must have an honest country to protect our liberty and be able to use it to build a glittering African nation,” the president said.

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