Understanding Bias in Forensic Science

Forensic science is the use of the scientific method and interdisciplinary scientific techniques to investigate crimes, identify and examine crime scenes, and present evidence in a criminal trial. Stories of early forensic investigations can be found as far back as 1248 in China with rudimentary techniques proving useful in solving simple crimes. In the 16th century European medical practitioners began to lay the foundations of modern pathology, the study of injury or disease, and in the 18th-century criminal investigations became more evidence-based.

One of the fundamental underpinnings of forensic science throughout time is that the techniques must be scientifically rigorous and any evidence found must be presented truthfully and unbiased. In many ways, the credibility of the evidence depends upon the integrity of the forensic scientist. Unfortunately, questions have been raised over the years about the accuracy of various forensic techniques, training requirements of forensic scientists, and subconscious bias.

Bias in Forensic Science

Despite continuous advances, forensic science grapples with a history of unscientific methods and scientific errors leading to wrongful convictions. Many techniques that were once commonly employed have fallen out of favor, including polygraph tests (“lie detectors”), bite marks, and burn pattern analysis. However, new reports have also explored the potential for bias to influence the decisions made by forensic scientists.

Bias, defined as prejudice in favor or against a thing, person, or group, can lead forensic investigators to make incorrect judgments or interpretations of evidence. For example, confirmation bias can result in a forensic scientist perceiving motives or beliefs from a suspect, leading them to alter their analysis of the evidence. Unfortunately, while many forensic experts are aware of this potential influence, many others believe that they are immune to it.

A recent study by cognitive psychologist Itiel Dror has added additional evidence by suggesting that forensic pathologists can be biased in their determination of murder versus accidental causes of death. Dror found that pathologists were more likely to pronounce a death as murder if the victim was black and brought to the hospital by the mother’s boyfriend compared to a white victim brought in by the grandmother. The author claims that these biases should be analyzed and understood – such biases can easily result in innocent people being put in jail. This is not the first time that Dror’s studies have brought about controversy. Earlier studies examined the role of biases information in fingerprint analysis and DNA fingerprinting, two methods long believed to be immune from such outside influence. It’s important to note that many prominent pathologists strongly refute the claims made in Dror’s studies, and it is unlikely that the issues will be easily resolved.

Special Agent Adam Deem, of Air Force Office of Special Investigation Detachment 219, shines light on a glass to reveal fingerprints at Barksdale Air Force Base, La., Jan. 18. Deem dusted the glass with an orange powder that helps agents detect finger prints with ultraviolet light. (U.S. Air Force photo/Airman 1st Class Micaiah Anthony)

Avoiding Bias in the Forensics Lab

There are many thoughts about how to avoid bias in the lab. One of the easiest methods might be to shield the forensic expert from any unnecessary information related to the samples, victims, and suspects. This is similar to how “blinding” works in a clinical trial – researchers are only given the most absolutely necessary information, often not even being aware of what treatment is being used on which patient. For example, a forensics expert might be first asked to analyze a fingerprint collected from a crime scene before then viewing potential matches (which are themselves blinded from any identifying information). Similarly, a pathologist might examine the cause of death independent of outside information as much as possible.

Finally, it’s important to discuss this topic with forensics students. Bias can be explored with any of the Edvotek Forensics experiments, allowing students to identify potential sources of bias and brainstorm methods to prevent it. This can include crime scene analysis and evidence collection (do the methods and thoroughness change depending on the type of crime?), data collection, and expert witness testimony. While these conversations can sometimes be uncomfortable, it is a valuable lesson for any future forensic scientist.

To read more about bias in forensic science we recommend the excellent summary by Science found here: https://www.science.org/content/article/forensic-experts-biased-scientists-claims-spark-outrage

Itiel Dror’s most recent journal article can be found here: https://onlinelibrary.wiley.com/doi/full/10.1111/1556-4029.14697

Cover image: You Only Get One Chance – Nuclear Forensics in Action. IAEA Imagebank.

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