Abstract

The impact of cognitive bias on decisions in forensic science has been demonstrated in
numerous disciplines such as DNA and fingerprints, but has not been empirically
investigated in the more objective domains, such as forensic toxicology. In the first
experiment, participants (n= 58) were affected by irrelevant case information when
analysing data from an immunoassay test for opiate-type drugs. In the second experiment,
participants (n=53) were biased in their choice of tests, for example, the age of the
deceased impacted testing strategy: for older people, medicinal drugs were commonly
chosen, whereas for younger people drugs of abuse were selected. Based on the results
that examiners analyzing case data may have biases if they are given access to case
context, we propose that examiners analysing presumptive test data are blind to irrelevant
contextual information. Furthermore, that forensic toxicology laboratories use a protocols
consistent, and that any deviations are documented and justified.