Effective and Ethical Expert Testimony

July 12, 2011

-Know the error rates of each measure/test used in the eval

-Know the research that the computer generated interpretation is based on (should be in manual)

-The trier of fact is your audience


-Always ask yourself: 

-How do I know this to be true?

-How do I know if it isn't true?

-If you were called by the other side, what would you have said? why?


-Experts make inferences, not factual statements

-Include alternatives you considered in your report

-Cite the opposing literature and then explain why don't agree with it

-Ask the attny who hired you what the opposing attorney's defense/evidence is

-Saying "I don't know" actually makes you more credible

-Say "I don't know and neither does anyone else" - when there's very litter research on that topic

-Be humble

-Answer hostile questions honestly

-If you weren't able to answer completely, ask the judge if you could complete your answer. Even if denied, it will be on the record that you weren't able to finish your answer

-Watch the jury/trier of fact - to see if they nod because they understand you, roll their eyes, etc. - normal conversation cues so you know how they're perceiving your testimony

-You want the jury to feel that you're being helpful to them - not so much the DA or defense attny

-State the limitations of your opinion before the opposing side can - makes you appear more credible

-Evaluation should always include both pros and cons for the defendant - never seen a case that's only all good for the defendant

-When attny wants to hire you, feel free to review the facts and directly say to the attny that he doesn't have a good case for you to eval- makes the attny respect you more

-If the opposing expert made a great point that you missed, just acknowledge it honestly if it comes up


Top 5 mistakes:

-only relying on info provided by attny

-forgetting that you are an advocate only for your opinions and methodology, NOT THE CASE itself

-putting too much in writing too soon and too casually

-being myopic

-sounding too much like an expert - make sure you can explain everything in layperson terms


The zen of expert testimony:

-you are evidence

-its not about you

-you're like a fingerprint (evidence) only less reliable

-nevertheless, be the fingerprint



Dvoskin, J. (2011). American Academy of Forensic Psychology Workshop Series, Portland, OR.

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