The film, 12 Angry Men, depicts the process that a group of twelve men undergo while serving as jurors for the trial of a young man accused of murdering his father. This drama offers several examples of cognitive bias, or an error in cognitive processes resulting from the perception of information through the lens of their own pre-existing beliefs. For example, confirmation bias has a pronounced effect on the perceptions of the evidence within the trial.
During the discussion between the jurors, the jurors are swayed to change their verdict through non-technical, readily apparent details about the evidence that created reasonable doubt, such as the witness who walked with an obvious limp. These details were visible during the trial to all twelve jurors, yet only one made any note of them. This demonstrates confirmation bias on the part of the jurors in that they only heard the information that confirmed their expectation that the young man from a rough part of town killed his father.
This process described above where the jurors selectively remembered confirming information also demonstrates another type of confirmation bias, the negativity effect. People are more likely to accept bad news as truth than they are good news. When the jurors heard the cases of both sides during the trial, they found it easier to accept that the boy killed his father because it was negative, further evidence that the world is getting more dangerous.
During the debate the jurors engaged in after the attorney’s closing statements, most of the jurors appeared to never consider that the young man would not kill his father. It was too obvious to their flawed perception that the bad news must be accurate, clear cognitive bias through the negativity effect.