How Psychology Expert Witnesses Can Impact Criminal & Civil Cases

Anjelica Cappellino, J.D.

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— Updated on April 30, 2021

How Psychology Expert Witnesses Can Impact Criminal & Civil Cases

Psychologists are highly trained in the study of the human mind and behavior. So it’s no surprise that they can offer unique perspectives in legal proceedings. For instance, psychology experts may testify about the mental state of a defendant or the psychological damages inflicted on a plaintiff. Through their specialized background, psychology expert witnesses are able to educate the fact finder on issues not readily discernible by other forms of evidence.

What Qualifies an Expert in Psychology?

Psychology is a varied field with many subspecialties ranging from forensics to counseling to cognitive behavioral therapy. Some psychologists work as health care providers and engage in the treatment of patients. Meanwhile, others conduct research and statistical analysis. Although deciding the ideal background for a witness will hinge on the particular subject about which they will testify, all expert psychologists should have the necessary educational requirements. Typically, this is either a master’s or doctorate degree in the field.

Postdoctoral residency programs, internships, and other clinical work are real-life experiences that most experts should possess. Furthermore, it is important to ensure that a practicing psychologist possesses the requisite licenses. Plus, they should be in good standing within their jurisdiction of practice.

Psychology Experts in Criminal Cases

In the courtroom, a criminal defendant will always be the focus for judgment. After all, the purpose of a criminal trial is to adjudicate a defendant’s guilt. In many instances, either explicitly or implicitly, psychological issues come into play. The most obvious situation occurs when a defendant directly puts their mental state at issue. This is done by either claiming that they’re incompetent to stand trial or not guilty by reason of insanity. During a competency hearing, psychology experts are tasked with determining whether a defendant can meaningfully participate in their defense. Although a judge makes the final determination as to competency, the decision is oftentimes reliant on the opinions of the expert witnesses.

The Insanity Defense

Psychologist experts also play an indispensable role when a defendant raises an insanity defense. Some jurisdictions, such as the federal courts, prohibit psychologists from stating whether a defendant did or did not possess the requisite mental state to commit the crime. Such an opinion would be considered an issue reserved for the trier of fact. However, the experts may provide observational or diagnostic opinions as to the defendant’s behavior, which can directly inform the fact finder of the ultimate issue.

The standard of proving insanity in the legal context is different from a clinician’s and varies throughout jurisdictions. Some states follow the M’Naghten test. This determines whether a defendant understood the nature and consequences of their actions. Other states look at whether the defendant was suffering from an overpowering impulse to engage in the criminal conduct. In either standard, a psychology expert witness can offer evidence in the form of data and studies in relation to the general issues. Psychology experts can also offer observations and reports on the defendant specifically.

A Defendant’s Mental Capacity

A psychology expert is not only helpful in the all-or-nothing, insanity defense context. There could be a scenario where a defendant is deemed competent to stand trial. But this defendant can still raise mental health arguments that could impact the case’s outcome. A defendant may argue that they committed the offense while suffering from a significantly reduced mental capacity that substantially contributed to the commission of the offense. Likewise, at sentencing, evidence of a diminished mental capacity may also increase the defendant’s chances of receiving a more lenient sentence.

Psychology Experts in Civil Cases

Though incredibly important in criminal cases, psychology experts are also critical in the civil context as well. Damages related to psychological conditions, such as emotional distress and pain and suffering, are becoming quite common when assessing compensatory damages. Sometimes, psychological injuries are longer lasting than the actual physical injuries (i.e., a car accident that resulted in the plaintiff suffering from post-traumatic stress). Although life-changing, a plaintiff’s psychological harm is not as easy to prove as a broken bone or laceration. This is why psychology expert testimony is critical.

Psychological Injuries

Psychology experts can provide evaluations and offer opinions as to the emotional impact the incident may have had on the plaintiff. Though experts cannot opine as to the awards amount, a psychologist can provide insight as to the plaintiff’s condition. Additionally, an expert may opine on how it will affect their day-to-day life both presently and in the future. From this information, a jury can more accurately glean a suitable damages amount.

Overall, psychology expert witnesses can offer an inner look into the minds of the parties. This can ultimately assist the trier of fact in coming to a decision. Whether in the criminal or civil context, a psychologist can help cases hinging on the mental conditions of either the plaintiff or defendant.

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