Why should not we believe unanimous opinion?

Agreement is very important in any community such as schools and companies. However, there are circumstances that doubt processes or systems that have come to the conclusion when "a perfect opinion agreement" took place. TED-Ed explains the state called "unanimous paradox" in an easy-to-understand animation.

Should you trust unanimous decisions? - Derek Abbott - YouTube


Suppose a bank robbery happens, a criminal has managed to narrow down suspects to several people somehow.


I ordered the suspects in a row and asked 10 witnesses to ask "Who did you see?", If six witnesses declare that the same one is the culprit, big hint Should be.


If 10 witnesses pointed to the same person, you might think that the case was as good as it was resolved.


But actually this is a mistake.


Our society consists mostly of "majority vote" and "consensus".


From the company meeting ......


Politics


To the world of entertainment including movies.


For that reason, consensus is becoming very important, but in reality there is a situation in which reliability decreases as the consensus of opinion approaches 100%. This is "unanimous paradox".


The key to understanding the unanimous paradox is that it is uncertain as a whole ... ...


Situation that it is included in certain circumstances.


For example, when there is only one apple in a banana, there is no funny thing even if apple is unanimously identified. This is because the difference between banana and apple is obvious.


On the other hand, when throwing 100 coins, the proportion of coins showing a table should be about 50%. Therefore, when the probability of the table approaches 100%, you should start to have doubts.


At this time, the one who should doubt not the person, the direction of the coin. There is a possibility that there may be a problem with the system that resulted in the result when "unanimous" happens to what is supposed to be a difference or inconsistency.


Of course, the act of "pointing to a suspect" is not as random as the throwing coin, but this is not as obvious as saying "to hit an apple in a banana."


As a matter of fact, in 1994 research, 48% of witnesses point to wrong suspects no matter how confident they are.


Since short visual information is easily deformed in memory, it is not reliable and reliable.


Therefore, unanimous conclusion in the identification of suspects,Systematic errorIt is happening ......


It seems that the suspect candidate seems to be biased.


The systematic error that an error occurs due to the method of measurement does not easily become apparent in places where human judgment is made.


Between 1993 and 2008, the DNA of the same female was detected in various parts of crime scene in Europe, and the mysterious culprit was "Heilbronn's PhantomIt was called. Since DNA is inspected precisely, it should not be wrong. For that reason, the investigation has been carried out for years to locate Heilbronn monster, but as we examine it, the fact that there are incompatible facts will come out.


Actually, DNA was attached to the cotton swab from which DNA was collected from the beginning.


In the cotton swab manufacturing factory work was done by hand, so the employee's female DNA was sticking to the swab. Heilbronn 's monster was an innocent general woman.


There was also a systematic error in Saddam Hussein's election held in 2002.


Hussein was trusted by the president at 100%, but, of course, this did not truly achieve 100% confidence, but there was a problem with the system situation.


Unanimity is not necessarily wrong. Unanimity will also happen as to the fact that there is little possibility of being clear and wrong.


However, unanimity does not occur in many scenes of the real world.


If there is a perfect agreement, there will be "hidden elements" that affect the system with a high probability.


No matter how hard we try to seek harmony ......


It is natural that errors and disagreements occur.


"Perfect conclusion" is rather unnatural, so you should try looking at suspicion once unanimity occurs at scenes where opinion differences may occur.