The Biggest Mistakes expert witnesses make, and how to avoid them

I see that Discovery is the theme for the Atlantic Provinces Trial Lawyers Association (APTLA) conference this June 10th and 11th in St. Andrews, NB. Specifically, The Art and Science of Discovery Examinations.

I don’t see much in the conference on mistakes expert witnesses make and how to avoid them. Yet there are a lot of them and I’m certain this will get attention at the conference. To be fair, nor have I seen a detailed outline of what the speakers plan to cover.

One source I studied identifies 220 mistakes based on research of the literature. A further 158 were suggested by trial lawyers, jury consultants and well known experts who were canvassed – 378 mistakes in total! On reading this material, I know I could add a few based on what I’ve seen over the years. I’m certain my colleagues in forensic work could as well. How about an expert taking a file on contingency?

A review of guidelines on expert report writing is certain to highlight more mistakes. There’s a lot of dos and don’ts. I didn’t want to get into overkill with more detailed research; a total of 378 mistakes is enough.

I see in the literature that the 220 mistakes can be partly categorized as follows with a few example mistakes taken from the many. Some mistakes are common, others are quite surprising to me and I’m sure to others:

  1. The Expert CV 2 example mistakes out of a total of 23 a) Mistake: Inaccuracies on a CV like misleading information b) Mistake: Listing past cases with results on your CV
  2. Web Pages 2 example mistakes out of 19 a) Mistake: Having inconsistent Web CV and paper CV b) Mistake: Listing innumerable areas of expertise
  3. Researching, Investigating, Forming and Expressing Opinions 3 mistakes out of 24 a) Mistake: Accepting rush cases that do not permit you to follow your standard protocol b) Mistake: Failing to document your work c) Mistake: Not corroborating facts provided by counsel
  4. Report Writing 4 mistakes of 32 a) Mistake: Letting counsel help write your report by sharing a draft with him/her b) Mistake: Basing the report on insufficient data c) Mistake: Using vague terms in the report d) Mistake: Allowing your word processing software to track the changes that you make to your report
  5. Depositions 3 mistakes of 31 a) Mistake: Taking notes at the deposition b) Mistake: Answering questions regarding a document you do not have in front of you c) Mistake: Being afraid to say “I don’t know”
  6. Direct Testimony 2 example mistakes out of 18 a) Mistake: Using terms that the judge and jurors do not understand b) Mistake: Getting outside your true area of expertise
  7. Cross Examination 2 example mistakes out of a total of 23 a) Mistake: Not advocating for your opinion b) Mistake: Giving new opinions on cross examination without careful reflection

There are more categories in the literature about the 220 mistakes but this is enough to illustrate the problem.

The 158 mistakes were presented differently, but with a little effort I’m sure they could be categorized in a similar way.

I believe APTLA are doing Yeoman service for their members in “…taking a deep dive into Discoveries” during the conference. I believe that the first promise during the dive to “…show you how to prepare your client” for Discovery would benefit from knowing about the 378 mistakes experts make.

I’ve dedicated my blog over the past 10 years to enlightening civil litigation lawyers, insurance claims managers and property owner to the nature and methods of forensic work. Drawing attention to the mistakes experts make is in tune with that resolve.


I thought on completing this blog that it would be helpful to study the 378 mistakes and identify those I’ve seen in Canada. Perhaps get my colleagues Down East to chip in what they’ve seen. The sources I checked are to U.S. publications and while helpful do not necessarily reflect completely on the situation in Canada.

(Posted by Eric E. Jorden, M.Sc., P.Eng. Consulting Professional Engineer, Forensic Engineer, Geotechnology Ltd., Halifax, Nova Scotia, Canada, April 25, 2022.   

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