Cognitive bias is a concept that has been recognized for centuries, with Francis Bacon discussing it in his Novum Organum in 1620. Despite its long history, it is only recently that cognitive bias has entered the forensic science arena. The Forensic Science Regulator produced a document in 2015, FSR-G-217, which illustrates the different forms of subconscious influence that exist and how they might come into play during a criminal investigation.
According to the Oxford English dictionary, “bias” has several meanings, including: “to influence, affect (often unduly and unfairly)”. No one likes to think of themselves behaving unfairly, and no reputable expert would ever regard themselves as anything other than a neutral advisor in an otherwise partisan system.
Dr David Schudel, a forensic chemist at Keith Borer Consultants, notes that subconscious influences were recognized a long time before the term “cognitive bias” was introduced to the forensic science community. He suggests using the term “subconscious influences” instead of cognitive bias to make the subject more palatable.
The concept of cognitive bias is still uncomfortable because no one wants to admit to being “biased” in any form, even if they can’t help it. This is why conversation about cognitive bias can be difficult, despite it being innate, unconscious, and normal.
There are several types of cognitive bias that can affect forensic science investigations, including expectation bias and confirmation bias. Expectation bias occurs when a person takes at face value what they expect to find, even if the evidence doesn’t support it. Confirmation bias occurs when a person ignores anything that contradicts their theory and looks only at the facts that support it.
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An example of expectation bias is a recent case where a defendant was charged with possession with intent to supply based on results from an accredited drugs laboratory. The offending substance was submitted to the testing laboratory on the assumption that a drug was present, and when results came back showing the presence of heroin, the prosecution team took it at face value, even though the substance didn’t match the typical characteristics of heroin in the UK.
Anchoring bias is another type of cognitive bias that can affect forensic science investigations. This occurs when a critical event at the start of a case anchors the investigation down a certain path, and what follows are confirmation and expectation effects that keep the case anchored to the same initial assumption.
In one case, fingerprints that matched a person on the fingerprint database were found at a school break-in. The accused person denied having been to the school and offered an alternative explanation, but the prosecution team was anchored to the initial assumption that the fingerprint belonged to the perpetrator. However, further analysis showed that the fingerprints were likely 15 years old, and the accused person had a plausible explanation for how they got there.
It is unimportant what type of subconscious influences are in play – what is important is to understand that they happen, and they affect everyone. As defence experts, Dr Schudel and his team are in a unique position to access the full range of scientific findings and assess them in the context of all of the case information, utilizing a problem that many experts face.
Critical findings checking and effective peer-review are important parts of protecting against subconscious influences. Dr Schudel urges caution when engaging the services of an expert who employs neither of these measures. If you have questions about forensic work done in your case, please get in touch with Keith Borer Consultants.