Confirmation Bias- The hidden danger to truth seekers

It’s midnight and your teenage son was supposed to be home by 10pm.  He finally walks through the door and there you are, seething mad (but also relieved) and ready to pounce on any excuse he gives you as to why he is two hours late.

The suspect in the burglaries you have been investigating for months is finally in custody.  He sits nervously in the interview room, awaiting your prepared line of questioning.  Your Detective Sergeant has been on your back about making an arrest in this drawn out and embarrassing case that has plagued your department for all too long.

The salesman finally returns from the manager’s desk at the car dealership.  He appears to be trying to look excited.  He is carrying a sheet of paper retrieved from the manager, likely with the supposed “best deal” they can offer on the vehicle that you have tried now for several hours to purchase.  You start to wonder how much they are going to try to take you for….

In each of the three situations you can find yourself in an emotionally charged situation.  It is vital in deception detection that you suspend any personal biases you may have.  Yes, its easier said than done.  I once worked a gruesome homicide case, in which the victim had been dismembered and had his skin filleted from his body (to remove tattoos that would identify him).  His body had been separated into several pieces and placed in different trash bags and subsequently thrown into the a river.  It was very difficult to not hold a bias against the two suspects as you can imagine.  Once you allow a bias into your interview/interrogation/torture session, you will set yourself up for failure.  Consider the following question:



Without cheating.. which card did you choose to flip?

The most popular answer is A and 4, with just A being the second most popular answer.  The correct answer however, is A and 7.  Why?  The statement does not say it is impossible for a consonant to have an even number on the other side.  An even number can have a vowel or a consonant.  It doesn’t state that an odd number can be on a card with a vowel or a consonant.  It only states that if there is a vowel on one side, then there is an even number on the other side.  Therefore flipping over the A should give us an even number.  It doesn’t matter what the D and 4 have- whatever the results won’t challenge the statements veracity.  Flipping over the 7 we should not get a vowel- if we do, then we disprove the statement. The statement says that the vowel must have an even number, so if the 7 has a vowel on the other side, the statement is incorrect because the vowel would have an odd number on the other side.

The reason it is difficult to solve the puzzle is confirmation bias.  This is the human brain’s tendency to seek information, facts and statistics that support it’s current position or known truth.  It takes us extra effort to seek out facts that will disprove our position, as flipping the 7 over would do.  How does this effect us in deception detection?  Simple- if we have supporting fact, knowledge or statistics that the person we are about to interview is guilty, we will have a strong tendency to give more regard to the facts supporting his guilt than we will give to facts supporting his innocence.  This is a terrible error.

In the three examples above there would already be several forces working against our ability to remain unbiased. The historical pattern of behavior of a teenage boy, a less than impartial boss and the known reputation of car dealerships (fair or not) to be less than honest when discussing purchase price.  However, it possible the teenager would have been home on time but experienced car trouble, the burglary suspect may have committed many burglaries in the past, but not the one you are investigating and the dealership really has reached the lowest price for which they are willing to sell the car.  And, as long as the possibility exists, we must give it equal weight of consideration.  If you go into these situations with bias, you will conclude with every gesture, expression or word that indicates deception that your suspect is indeed guilty while ignoring evidence to the contrary.  If you are able to suspend your bias and search for indicators that disprove your personal bias then you will have a clear view of the truth.  None of this means you should ignore indicators of deception, it simply intends that you apply equal consideration to the indicators of truth as well.


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