Ipse Dixit in Latin means, “he himself said it”; It is frequently encountered in expert testimony.
Ipse dixit is an unsupported statement that rests solely on the authority of the speaker. I think a better translation is “because I said it…[it is true].” It is a conclusory opinion without support.
Gutheil & Bursztjan (2003) articulate the theory that ethical expert witnesses are under appropriate burdens “to articulate carefully and thoughtfully the basis of the opinion and the reasoning process in reaching the opinion that is provided to the court.”
They note that a common problem is that in examining expert witnesses, “attorneys often fail to pursue questioning that brings out the basis for expert testimony beyond ipse dixit” (p. 207).
Junk science is expert opinion based on flawed, factitious, or idiosyncratic methodology” (p. 206).
The Specialty Guidelines for Forensic Psychology(2011) address this issue in a number of places. The spirit of the Specialty Guidelines is based on the Federal Rules of Evidence, and including the Daubert progeny, on the role of reliable and valid methods in both the form and the development of evidence.
Guideline 2.05: Knowledge of the Scientific Foundation for Opinions and Testimony
Forensic practitioners seek to provide opinions and testimony that are sufficiently based upon adequate scientific foundation, and reliable and valid principles and methods that have been applied appropriately to the facts of the case.
When providing opinions and testimony that are based on novel or emerging principles and methods, forensic practitioners seek to make known the status and limitations of these principles and methods.
Guideline 2.06: Knowledge of the Scientific Foundation for Teaching and Research
Forensic practitioners engage in teaching and research activities in which they have adequate knowledge, experience, and education (EPPCC Standard 2.01), and they acknowledge relevant limitations and caveats inherent in procedures and conclusions (EPPCC Standard 5.01).
9. Methods and Procedures
Guideline 9.01: Use of Appropriate Methods
Forensic practitioners strive to utilize appropriate methods and procedures in their work. When performing examinations, treatment, consultation, educational activities, or scholarly investigations, forensic practitioners seek to maintain integrity by examining the issue or problem at hand from all reasonable perspectives and seek information that will differentially test plausible rival hypotheses.
Gutheil & Bursztjan note the disturbing research findings that 80% of jurors make up their mind after opening statements (p.208).
Consequently, they note the requirement that “a substantial part of an expert’s efforts in a case precede trial testimony and are directed toward educating the attorney…” (p. 208).
Finally, they write that the expert’s role is “to aid attorneys to prepare their opening statements adequately in a manner that validly, accurately, and effectively presents their own expert’s opinions; anticipates weaknesses; translates expert opinions into common language; and critiques any lack of intellectual rigor in opinions by opposing experts” (p. 209).
APA (2011). Specialty Guidelines for Forensic Psychology.
Gutheil, T., & Burstjan, H. (2003). Avoiding the Ipse Dixit Mislabeling: Post-Daubert Approaches to Expert Clinical Opinions. Journal of the American Academy of Psychiatry & Law, 11, 2, 205-210.