Forensic Science Regulator guidance: Cognitive bias effects (2020)

Summary

Cognition is the mental process of knowing, including awareness, perception, reasoning and judgement, and is distinct from emotion and volition. Cognitive processes include mental shortcuts, which speed up decision making. However, cognitive bias occurs when the shortcut causes inferences about other people and/or situations to be drawn in an illogical fashion.

There is a tendency to display bias in judgements that are made in everyday life, indeed this is a natural element of the human psyche. Jumping to a conclusion, tunnel vision, only seeing what is expected/wanted, being influenced by the views of others, all are recognisable behaviours. However, whilst such biases may be commonplace and part of human nature, it is essential to guard against these in forensic science, where many processes require subjective evaluations and interpretations. The consequences of cognitive bias may be far-reaching; investigators may be influenced to follow a particular line of enquiry or interpretation of a finding that may be incomplete, or even wrong.

Simply because there is a risk of a cognitive bias does not imply that it occurs. The problem is that as it is a subconscious bias it is unlikely that an individual will know either way and therefore it is wise that all practitioners understand the issue and take proportionate steps to mitigate against it.

Content

There are a number of categories of cognitive bias described in more detail in these guidelines:

1. Expectation bias, also known as experimenter’s bias, where the expectation of what an individual will find affects what is actually found.
2. Confirmation bias is closely related to expectation bias, whereby people test hypotheses by looking for confirming evidence rather than for potentially conflicting evidence.
3. Anchoring effects or focalism are closely related to both of the above and occur when an individual relies too heavily on an initial piece of information when making subsequent judgements, which are then interpreted on the basis of the anchor.
4. Contextual bias is where someone has other information aside from that being considered, which influences (either consciously or subconsciously) the outcome of the consideration.
5. Role effects are where scientists identify themselves within adversarial judicial systems as part of either the prosecution or defence teams. This may introduce subconscious bias that can influence decisions, especially where some ambiguity exists.
6. Motivational bias occurs where, for example, motivational influence on decision making results in information consistent with a favoured conclusion tending to be subject to a lower level of scrutiny than information that may support a less favoured outcome.
7. Reconstructive effects can occur when people rely on memory rather than taking contemporaneous notes. In this case people tend subsequently to fill in gaps with what they believe should have happened, and so may be influenced by protocol requirements when recalling events some time later from memory.