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ASU researchers debunk 'junk science' found in court testimony

Both legal and psychological professionals should scrutinize evidence, researchers say


"Psychologists use tested methods to evaluate someone's mental state." Illustration published on Tuesday, Feb. 25, 2020.

Forensic science provides necessary evidence in legal settings, but many methods once considered credible have been proven inaccurate after being used in countless court cases. 

Tess Neal, an assistant professor of psychology at ASU, found that evidence based on forensic psychology largely escaped scrutiny both in the legal and psychological communities.

From the beginning of her career, Neal has been passionate about forensic mental health evaluations. Her interest led her to see how little others looked into the details of expert psychological testimony.

Neal led a study of common tools psychologists use to evaluate someone’s mental state, hoping to address the distinct lack of information about the methods.

“I feel good knowing that other people can see the good and the bad with the field,” Neal said. “Today if we can understand the limitations of the current standard of practice, then we can do better.”

Researchers used survey responses from psychologists to compile a list of over 300 tools used in evaluations. They examined 30 of these tools to determine their popularity among experts and their scientific credibility.

Psychologists use tested methods to evaluate someone's mental state. One of the most famous tools is the Rorschach test, in which a psychologist analyzes a patient's interpretation of inkblots on paper. 

Researchers at ASU, Vanderbilt University, UC Hastings and Pennsylvania State University collaborated on the study. The team debunked several popular tools psychologists use in court but also found many of these inaccurate methods were frequently utilized by specialists.

The study found that long-discredited methods are still commonly used by psychologists in court. Some experts even reported abandoning established methods altogether and using only their personal intuition to make a decision. 

Mental health evaluations can happen in court for numerous reasons. Those include verifying an insanity claim, evaluating someone’s ability to represent themselves or determining someone’s competence. 

Neal and her fellow researchers found that lawyers and judges are not adequately challenging the credibility of the evidence presented. 

Michael Saks, a professor of law with the Sandra Day O'Connor College of Law, said the United States' system of choosing experts leaves little safeguards for credible evidence in the court. 

Saks said although it is the judge's job to assess the validity of witness testimony, they are unlikely to do that unless a lawyer challenges the matter. 

Saks also said in the U.S. legal system defendants and prosecutors can hire their own experts. Saks said this can trigger something called "allegiance bias" in the expert. Allegiance bias is the unconscious desire to take the side of people with whom you are associated, like an employer. 

Judges will wait for lawyers to challenge a matter, but lawyers rarely do, according to Saks. He said the inaction towards forensic psychology in the court also affected the way experts see their testimony.

"That tells you that pretty much whenever the experts want to do, they can do with very little fear of anybody questioning the appropriateness of a tool that they're using," Saks said.

Expert testimony is important because having a scientist clarify the complicated parts of evidence to the jury allows them to make an informed decision on the case, according to Saks. 

“When you're using expert witnesses, you want witnesses who can help you process and better understand the meaning of what happened,” Saks said. “So maybe I have some blood. It's easy enough to collect some blood at a crime scene, but to try to say whose blood was that, we're going to have to get an expert.”

Saks said restructuring could provide systems of checking biases, but that is a huge task for a large institution whose resources are already strained. Both Saks and Neal expressed hope that their findings can guide people to better practices in vetting evidence.

Neal said one paper doesn’t usually change an entire scientific field, but this area is under-researched and her work could have a significant impact.

“I hope that it encourages the legal system to do a little more challenging when appropriate,” Neal said. “I hope it encourages psychologists to realize that people are looking, and people should have an appropriately skeptical view.” 

Neal said this paper will also be a great resource for the general public. The study is open source, meaning it is available to anyone for free on the internet, and all U.S. citizens are called for jury duty in their lives. She said these findings could help put evidence into perspective for future jurors.

“If people are going to be paying attention to what you're doing then you need to do the best that you can,” Neal said about psychologists who testify in court.

Neal thinks much of the responsibility to scrutinize psychological evidence falls on psychologists themselves. She said that other fields frequently debunk their own practices through introspection and that psychology should be treated the same.

Emily Line, a graduate student of psychology who worked as a research assistant on the project, said she initially came to ASU because she was so interested in Neal’s research focus. She said working on the project was a great opportunity for her and gave her insight into forensic psychology. 

"Students have a really great opportunity to see how the nitty-gritty part of research works," Line said. "It's not just about writing papers and analyzing data, there's a lot of work that goes into the front end of getting the data."

Line said that the project was made possible by a hard-working team, and she was happy to experience the efforts. 

"It takes a lot of effort and Tess was able to bring a lot of people together a lot of people help her with that effort, so it was cool to be a part of that," Line said.  

Neal and other researchers speculated that their identification of the problem is a first step towards improving the quality of methods in forensic psychology.  

Reach the reporter at or follow @G_Mira_ on Twitter. 

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