background

• confirmation bias


  this occurs when people observe more, give extra emphasis to, or intentionally look for evidence that would validate their current beliefs.
• tversky and kahneman 1974

  identified several different types of bias in forensic analysis

  • observation or expectancy bias
  • conformity effect/conformity bias
  • overconfidence bias
  • contextual bias
• observer or expectancy bias


  this is when the expert anticipates the outcome as a result of information from an initial observer and therefore has preconceived expectations about the outcome
• conformity effect/conformity bias


  if a fingerprint expert is asked to validate the decision of a peer, or a superior, this effect may unconsciously bias them to agree with the original decision if they are aware of it
• need-determination perception


  this bias arises from a strong desire to solve a particular crime
• overconfidence bias

  experts may experience overconfidence bias and this may make them believe that they are always right, even in the face of contradictory evidence. the more experienced and intelligent they are, the easier it is for them to defend their biases and beliefs
• contextual bias


  a scientist working within a police laboratory could be influenced by knowing that detectives believe that they have a strong suspect, or that the suspect has already confessed to having committed a crime
• dror et al 2005


  they gave university research students either good quality or incomplete, poor quality fingerprints to study. they were also given emotional stimuli deemed low level or high level. the latter was accompanied by distributing photographic images of the victim. some volunteers were also subjected to subliminal messages stating 'guilty' or 'sane'. the results showed that the volunteers were affected by the emotional context and this interfered with their decisions, making them more likely to make matches