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 Justice Scales


Information that bypasses awareness can still influence decision making. While information is processed in this way to maximise limited cognitive capacities, one consequence is that people are not always aware of all of the factors that guide their decisions. Decision making is therefore susceptible to the influence of irrelevant factors and preconceptions, which can lead to suboptimal reasoning. The unintentional reasoning errors that people systematically make are collectively known as ‘cognitive biases’. Psychologists have identified a large number of cognitive biases some of which have been studied in the court setting and they are discussed in this paper:

  • Confirmation bias occurs when people seek, weigh or interpret information in a way that conforms to their pre-existing beliefs or assumptions. For example, mock jurors who endorse statements about the leniency of the justice system tend to favour conviction in a burglary case at a higher rate than those who do not.
  • Contextual bias occurs when information about the context of an event, or the way in which some information is presented, influences reasoning but is logically irrelevant to the decision at hand. For example, the presence of routine, day-to-day contextual information (such as whether the suspect has an alibi) can influence the results of forensic fingerprint identification. Read more about this bias in the POSTbrief , Unintentional Bias in Forensic Investigations.
  • Unintentional stereotype bias occurs when people associate certain traits with their perception of a person’s social group, such as race, gender or age. These associations can influence decisions and behaviour, even though people are unaware that they harbour them. For instance, in a video-game simulation, US police officers tended to shoot unarmed black suspects at a higher rate than unarmed white suspects, an effect known as ‘weapon bias’.

Psychologists are working with the judicicary on approaches to minimise the effect of these biases. You can find out more about this on Dr Tom Stafford’s blog. Tom has blogged about his recent work with employment tribunal judges.


  • Assumptions, stereotypes and contextual information can influence judgement unintentionally, and result in suboptimal reasoning.
  • Studies show that this affects decisions of forensic experts, witnesses and mock jurors.
  • As most people are unaware of their cognitive biases, they are hard to control, but their effect may be mitigated by a variety of targeted strategies.
  • Training judges and educating jurors may reduce the influence of cognitive biases in court.

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