The Controversy Surrounding "A Reasonable Degree of Psychological Certainty" in Forensic Testimony
In the world of forensic psychology, one phrase often comes up during court testimony that can cause discomfort even among seasoned professionals: “to a reasonable degree of psychological certainty.” Attorneys commonly ask forensic psychologists this question when they are on the stand, expecting it to lend scientific weight to their conclusions. However, this seemingly authoritative phrase is fraught with ambiguity and potential problems.
While it sounds scientific, the term “a reasonable degree of psychological certainty” is not as concrete as it may seem. Unlike medical or legal standards that have clearer definitions, what constitutes "psychological certainty" is poorly defined in the field of psychology. This ambiguity can be troubling for experts who are expected to provide clear, objective testimony. In fact, many psychologists, myself included, find the term problematic because it invites subjective interpretation rather than promoting precision and clarity.
One challenge with this phrase is the lack of consensus around what a “reasonable degree” actually means. What is "reasonable" to one expert might not be "reasonable" to another, leaving the term open to interpretation by both forensic psychologists and the legal system. The concept of "certainty" in psychology is equally elusive, as psychological diagnoses and evaluations are rarely as clear-cut as one might assume. Mental health assessments often involve interpreting complex human behavior and subjective experiences, which makes the idea of psychological “certainty” difficult to pin down.
In some cases, forensic psychologists can support conclusions with a strong differential diagnosis and a thorough review of all available data. This involves ruling out alternative explanations and narrowing down possibilities based on objective testing, interviews, and record reviews. In these instances, a psychologist might feel comfortable stating their conclusions to a "reasonable degree of psychological certainty" because they have ruled out other plausible explanations for the individual's behavior or mental state. This structured approach lends more credibility to the concept of psychological certainty by backing conclusions with substantial evidence.
However, even in cases with solid data, the term remains problematic because it can be used too loosely. Without a universal definition of what "reasonable" or "certain" means in psychological practice, courts may take this language at face value without understanding its limitations. Forensic experts must be careful not to overstate their conclusions, particularly when the evidence is open to multiple interpretations or when alternative diagnoses cannot be fully ruled out.
Forensic psychologists need to consider carefully whether they feel comfortable answering the “reasonable degree of psychological certainty” question before stepping into the courtroom. Experts should be prepared to clarify the limitations of their assessments and avoid giving the impression of absolute certainty when psychology, by its nature, is a probabilistic science.
In essence, the term “reasonable degree of psychological certainty” is misleading because it gives the appearance of a clear-cut scientific standard that doesn’t fully exist in psychology. While it can sometimes help convey a level of confidence in a forensic opinion, it is vital for forensic psychologists to navigate this language thoughtfully, ensuring that the court understands the nuances and limits of psychological evaluations. Transparency about the limitations of our findings, rather than the use of nebulous terminology, is the key to maintaining both the integrity of our work and the fairness of the legal process.
