Friday, February 19, 2016

The truth about the polygraph

Would I be lying if I said that Wonder Woman's lasso of truth was based on the polygraph test? Would you know if I was lying?
Would you be lying if you said that you knew I was lying?
Last week I attended a lecture by the Professor Emeritus of Forensic Psychology from the University of Newcastle. The subject of the lecture was polygraph testing in the forensic setting, the slightly more interesting aspect of the lecture was that it was given by an American who is very pro polygraph testing when used correctly and in appropriate circumstances while being rather bemused that the British don’t get it simply because there is something rather unBritish about the lie detector.

He explained that in America lie detectors are used for all kinds of job interviews especially when there is a degree of security involved, banks some law enforcement applications etc. In Britain we just take your word for it as there would be something rather unseemly in giving someone a polygraph.

So on this side of the pond we are a bit far behind and even articles in respected newspapers are always fundamentally flawed in their facts and this reinforces the fallacies that the British public have about lie detectors.

The three big lies are;
 1) It didn’t work in the 1950's and it doesn’t work now 
2) It is a bogus pipeline to the truth 
3) The test can be easily beaten. 

None of these are true.


If you are not familiar with it the polygraph is now a small box about the size of a box of man sized tissues. It has a chest strap, a belly strap and a blood pressure cuff with the clamp electrode on one finger. This measures chest and abdominal breathing, cardiovascular activity and sweating. These changes are not specific to lying, they are simply of arousal. It is not a narrow defined stress response it is more an arousal to threat which psychologists call the 'orientating response'.

I  would explain that  as this not being the stress response you have when someone points a gun at you. This is the response you have when walking through a dark forest and you hear a noise that may or may not be a threat. All your senses then pinpoint where that noise came from, focussing on where the threat actually is,  and that is the method of the lie detector. The brain is scanning the situation waiting for the question that is going to cause the threat.
The Brits still believe that the polygraph measures the stress of trying to lie convincingly and therefore it can be beaten if  you have very good relaxation/biofeedback techniques or are a psychopath. But as the orientating response is a much more primal response, much deeper in the brain and is therefore hard wired so the relaxation biofeedback the psychopath has the same response on a polygraph as everyone else.

Here is Ramsay's version of an interesting experiment they did;

Let's  take the Europeans and South Africans of the MIA blogsite and put them in one room (I’m taking Cara as a French person in this). So we have the combined loveliness of Cara, Caro, Zoe, Jorn, Michael and Stanley in one room. In the other room we have the 'Donald Trump non appreciation society' of Annamaria, Jeffrey etc. Just to make Annamaria’s life difficult we’ll put Evka in that room as well.

The person conducting this experiment knows that the European team will not cheat under any circumstances as they are honourable Europeans. So, the researcher takes one of the American team to the side and charges him $20 for the answers to the exam paper. Both classrooms then sit the same exam and at the end of the exam in the US classroom the cheater stands up and reveals he had all the answers all along and cheated. He asks his fellow US students not to say a word. The Europeans have now become the control group. The  Americans become the subject of  the experiment. All the students are then told that they are going to be polygraph tested and will be asked if they knew of any cheating going on. No matter how many times this experiment is done the results are consistent.

If the students are told the polygraph is 40% accurate, the Americans will lie to protect their friend. If they are told it is 70% accurate they will still (tend to ) lie to protect their friend. However if they are told that the polygraph accuracy is getting towards 75% then people begin to disclose even before the polygraph is switched on. And as polygraphs are between 85 and 92% accurate there is a tendency toward full disclosure and it is the disclosure aspect of the polygraph that is of most use in focusing the resources of a criminal investigation.

Dr Don Grubin has been using this technology in a very worthwhile way but stresses again and again that the polygraph has no place in court. It is this ability of it to force people to disclose activity that is important.

In the South of England he has conducted many interventions  and I am using the example of 60 men who have been shown to have child pornography on their computers. These 60 men were told that they were going to be given a polygraph test and that the polygraph test is between 85 and 92% accurate and of the 4 indicator questions allowed one of them was 'have you ever tried to make contact with a child for sexual purposes?' 7 of those men then disclosed immediately even before being given the test and that group then became subject to further investigation. All the men were polygraphed and the results of the indicator questions tended to replicate the disclosure result.
The lecturer explained that there is always a tendency for there to be more false failures than false positives so its not a case that dangerous people will slip through the net but more that slightly less dangerous people are going to be caught up.

Even after this very eminent Prof explaining how the polygraph can be used accurately and ethically the very esteemed prosecutors and defence lawyers in the audience immediately started to argue with him that it was in some ways a downright dastardly thing to do. I am glad to say that the Prof defended the polygraph robustly.

There was  a bit of lovely humour when he showed a clip from the TV series the Wire to which the audience murmured uniformly we didn’t watch it that as we could not understand the accents. And the American replied the Baltimore accent is nothing compared to the Glaswegian accent. 

And of course, William Moulton Marsden created Wonder  Woman and the lie detector!  So there!

Caro Ramsay 19th Feb 2016


  1. Very informative, Caro. But I have one major gripe. I claim Cara and Stan for the American team. Otherwise I will be left alone with Jeff and EvKa and will surely die of pun poisoning. My life is on the line here.

  2. I was thinking that you could have Susan and Sujata but yes I agree, it would be too cruel to subject you to the J and E punfest. But you would disclose your secrets just at the threat of Jeff and EvKa, so it would all work out ok!

  3. This seems a very boring experiment for the 'European' team. Maybe we should lie about having the test just to make it more interesting!

  4. It would not be boring in the European room Michael. After getting full marks in the test we could sit around, draw rude pictures of teacher on the board and make paper aeroplanes. Well, it never did me any harm!

  5. Fascinating column, Caro, at least the part I've gotten to. I'll read the rest when I'm done staring at Linda Carter...

    What I think the police REALLY need is a lye detector, since that is the preferred method of body disposal by more intelligent murderers.

    All joking aside, I think the efficacy of the lie detector could be raised to nearly 100%, at least for male subjects, if Linda Carter were the test administrator. I'm convinced she'd have not trouble causing them to make a clean breast of it.

  6. And that EvKa is why you will be in the American part of the experiment!
    But I agree that anybody faced with those huge blue pants (British use of pants) would probably 'fess up before they fall over laughing. Or is that just a female point of view...

    1. No, I think only a man could possibly design an 'outfit' like that one. At least, any woman that came up with that should have their membership card revoked. Men... well, we're all idiots and are expected to behave as such.

  7. Frankly, I'm shocked and appalled at the behavior of my American male teammate. How could he possibly ignore the arousal measurement capacity of Wonder Woman's lasso of truth and settle for making himself a boob. Shame on you EvKa.

    1. I cannot lie. I am completely and udderly ashamed. Please don't tell anyone else. I'd be destroyed were I ostracized, were a gap or cleavage to form 'tween me and my bosom companions. I need your full support, Jeff, or I shall sag in the flesh as I have in the mind.

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