Factors affecting someone’s judgement

Someone who aims to tell the truth, and who is in a position to have the relevant knowledge
may nevertheless be unreliable because of circumstances which interfere with the
accuracy of his or her judgement. For example, emotional stress, drugs and alcohol can
affect our perceptions. We can be distracted by other events which are happening concurrently.
A parent with fractious children in the car may notice less about a road accident
than someone who is travelling alone. We can forget important aspects of what has
happened, particularly if some time elapses before we report an incident. In the case of
people gathering and assessing evidence, for example scientists and psychologists, the
accuracy of their observations and interpretations can be affected by their strong
expectation of a particular result, or their strong desire to have a particular theory confirmed.
Expectation and desire can also play a part in evidence provided by people who
have prejudices against particular groups or individuals, so we need to be aware that
prejudice may influence someone’s belief as to what they saw or what happened.
Corroboration
Sometimes when we have evidence from more than one source, we find that two (or more)
people agree in their descriptions of events – that is to say, their evidence corroborates
the statements of others. In these circumstances, unless there is any reason to think that
the witnesses are attempting to mislead us, or any reason to think that one witness has
attempted to influence others, we should regard corroboration as confirming the reliability
of evidence.
Summary: assessing reliability of evidence/authorities
Here is a summary of the important questions to ask yourself about the reliability
of evidence and of authorities.
1 Is this person likely to be telling a lie, to be failing to give full relevant
information, or to be attempting to mislead?
• Do they have a record of being untruthful?
• Do they have a reason for being untruthful?
• Would they gain something very important by deceiving me?
• Would they lose something very important by telling me the truth?
2 Is this person in a position to have the relevant knowledge?
• If expert knowledge is involved, are they an expert, or have they been
informed by an expert?
• If first-hand experience is important, were they in a position to have that
experience?
• If observation is involved, could they see and/or hear clearly?
3 Are there any factors which would interfere with the accuracy of this person’s
judgement?
• Was, or is, the person under emotional stress?
• Was, or is, the person under the influence of alcohol or drugs?
• Was the person likely to have been distracted by other events?
• Does the person have a strong desire or incentive to believe one version of
events, or one explanation, rather than another?
• Does the person have a strong prejudice that may influence their beliefs
about events?
• In the case of first-hand experience of an event, was information received
from the person immediately following the event?
4 Is there evidence from another source that corroborates this person’s
statement?