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Asking Expert Witnesses for an Opinion ‘to a Reasonable Degree of Certainty’ Redux

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Written by NITA guest bloggers Iva Čechráková and Michael J. Dale

A question has recently arisen regarding the rationale or basis for the use of the phrase “to a reasonable degree of certainty” in California. The question was posed, based upon our June 20, 2018, blog post, Why Do Lawyers Ask Expert Witnesses For An Opinion “to a reasonable degree of medical certainty”? The answer appears to be similar to what we discovered in other jurisdictions: it is tradition.

Jeff L. Lewin in his article on the subject describes the evolution of the term and the process by which the phrase spread into other states from Illinois.1 Referring to, among others, courts in California, Lewin stated that “the appellate courts simply quoted or paraphrased the trial testimony, and such cases merely reflected that attorneys in the jurisdiction were using the phrase.”2 At another point, the author, making a comparison with courts in different states where the courts endorsed the use of this phrase, seems to have encouraged its use.3

The answer in California appears to be twofold. First, California is among the states that do not have a relevant statute incorporating the phrase. Second, research discloses no reported California case discussing the reason for the use of the phrase. Rather, a substantial body of California case law, like reported opinions in other jurisdictions, simply refers to the phrase without explanation.


Iva Čechráková is a graduate in law from Charles University, Prague, Czech Republic, and a dual degree graduate of Nova Southeastern University College of Law, where she was until recently a research assistant to Professor Michael J. Dale. She is currently working for the White and Case law firm in Prague and can be reached at

Michael J. Dale has been a member of the faculty at Nova Southeastern University Shepard Broad College of Law since 1985. He teaches regularly for the National Institute for Trial Advocacy. He can be reached at If you’d like to know more Professor Dale, please read his “Asked and Answered” interview with The Legal Advocate here.

To read more articles by Professor Dale’s research assistants at Nova Southeastern, click here.

1 Jeff L. Lewin, The Genesis and Evolution of Legal Uncertainty About “Reasonable Medical Certainty,” 57 Md. L. Rev. 380, 439–40 (1998).
2 Id.
3 Id.

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