Your Day in Court: Becoming an Effective Expert Witness

TrialAs scientists, we’ve all have those moments when we are asked to explain to a nonscientist—maybe Mom or Grandpa—what it is we do all day in the lab. Or maybe someone asks us a seemingly innocent question such as “How can DNA be used to identify someone?” Do you try to teach them about polymorphic DNA sequences, population genetics, PCR, capillary electrophoresis, the necessary statistical calculations and all of the other factors involved? Even if your audience members are patient enough for that, will they understand, or will their eyes glaze over after the first 10 minutes? If you’re like me, you give your inquisitor the high-level, 30,000-foot overview of the topic and hope that that is enough to satisfy their curiosity. Answer the question, but don’t get bogged down in too much detail unless your audience really seems genuinely interested in delving further.

That’s all fine and good if you can get away with that approach, but there are situations where the high-level overview won’t suffice.

You’re on the hot seat, and your inquisitor is mercilessly pushing you to explain things in detail and defend your scientific method. You might be reminded of your thesis defense or a similar presentation that you had to give, but at least those audience members had a good grasp of science. A better example might be an expert witness in a trial, presenting DNA-typing results to judges, lawyers and a jury of people who may have little or no formal science education beyond high school. As the expert witness, you must be prepared to explain the labwork—the DNA purification, amplification and capillary electrophoresis—but also data analysis and interpretation, including complicated statistical concepts such as the Hardy-Weinberg equation, likelihood ratio, power of discrimination, mixture interpretation and random match probability. You must convince your audience that you did the analysis properly and arrived at the correct conclusion despite the fact that attorneys may try to cast doubt on any evidence that doesn’t work in their favor. It all sounds very daunting.

Testifying in court as an expert witness need not be stressful, but it does require a lot of preparation. You must be able to present your findings clearly and impartially, communicate any limitations of the analysis and explain any anomalies that you encountered. While you’re reviewing your case file and preparing for your own testimony, you may be called upon to help the attorneys prepare as well. What’s the best way to get ready for your day in court?

For starters, you can attend the Expert Witness Testimony workshop at the upcoming International Symposium on Human Identification. This workshop is hosted by legal and DNA-testing experts to answer your questions about case law and expert witness testimony and advise you on the most effective ways to prepare for your day in court. You won’t want to miss this opportunity to gain from their experience.

The following two tabs change content below.

Terri Sundquist

Terri has worked as a Scientific Communications Specialist at Promega Corporation for more than 13 years, and prior to that, spent more than 5 years solving problems and answering questions as a Promega Technical Services Scientist. She graduated with B.S. degrees in Chemistry and Biology at the University of Wisconsin—River Falls, then earned her M.S. in Molecular Biology from the Mayo Graduate School in Rochester Minnesota.


  1. I am so very excited you posted this! In my experience attending forensic seminars and classes in identification they rarely go over “expert witness testimony” and what you should be prepared for. I wish more schools would dedicate a class to this one subject for those of us interested in forensics or criminal justice.

  2. I agree, ohthesanity. I’ve heard many analysts say that they’d love to have more training on this subject so that they are better prepared and more confident in the “hot seat”. I expect this workshop to be quite popular with ISHI attendees, not only with analysts just starting out but also with experienced analysts with specific concerns or questions.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.