Certain areas of weakness attend some expert testimony. Those areas will certainly be the grounds for attack by a cross-examining attorney. Knowing the following areas of jeopardy will help the expert prepare in advance for the cross-examination.

1. Is the expert's opinion based in whole or in part on judgment as opposed to measurable fact? It is always proper for cross-examination to probe the basis for the expert's well-established conclusions. If that basis is technical and scientific testing, the expert will not be vulnerable. However, if subjective judgment and opinion are the sole basis for the expert's opinion, the expert is vulnerable.
2. Is the expert's opinion based on input from others?
3. Has the expert made prior inconsistent statements? The questioner will ask about whatever the witness may have written and testified to in the past. Aggressive cross-examining counsel will comb those written materials for inconsistency.
4. Does the expert's behavior suggest insecurity? The skillful cross-examining attorney will observe the expert witness carefully. A hand near the mouth or face may suggest a witness withholding information, according to the attorney's way of thinking. If the expert flushes or a hand trembles, that may signal insecurity. If the expert hesitates and stammers or fumbles through papers and files, that may betray a lack of confidence in ability. Skillful examining attorneys sense a weak, inadequately prepared or unsure witness.
5. Is the expert in control? The basic tenet of cross-examination for the attorney is control of the witness. Therefore, the expert must stay in control and resist being led by the cross-examiner. A pattern of yes/no questions and answers should warn the expert that the examining attorney is attempting to control the situation. But the expert has another option besides a "yes" or "no" answer.
   
   Question: "Mr. Expert, isn't it correct that traffic lights sequence green to yellow to red?"
   
   The easy answer to the question is "Yes," but the better answer is "Yes, in most cases, unless there is a malfunction." In this way, the expert has avoided the trap of a yes/no answer.
6. The expert should make sure that the theories on which testimony and conclusions rely:
   • a. Are relevant to the case.
     b. Rest on a reasonably reliable foundation.
     c. Meet the conditions in Daubert (testing, peer review, error rates and "general acceptability") or Frye, depending on the jurisdiction.

The usual admonition for cross-examining counsel is to:

• Stop when ahead.
• Use restraint.
• Do not overplay.

The same admonitions are equally true for the expert witness undergoing cross-examination. The testifying expert should:

• Not overplay the expert role.
• Not overemphasize superior knowledge.
• Be accurate with the facts.
• Be firm without being an advocate.
• Maintain control of the situation.

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