The way psychologists and psychiatrists approach their roles as expert witnesses also varies. Psychiatrists often provide testimony on how psychiatric disorders, substance abuse, or medications may influence a person’s behavior or decision-making abilities. For example, in a criminal case, a psychiatrist might be called upon to explain whether a defendant’s mental illness could have impaired their ability to understand right from wrong at the time of the offense. On the other hand, psychologists are more likely to focus on behavioral assessments, cognitive functioning, and personality evaluations. They might conduct in-depth psychological testing to determine competency to stand trial, assess trauma, or evaluate the long-term impact of mental health issues in civil cases such as personal injury claims.