In the forensics context, the impeachment may be an attack on the science or the conclusions rather than on the expert.

The expert must be prepared to acknowledge lab error rates, or errors in or limitations of the science or technology. An attempt may also be made to show that the expert was not provided with all of the facts by the attorney or that the expert failed to consider additional circumstances.

Finally, where the expert is employed in a police or government lab, it is likely that some attempt will be made to show a collusive or at least collaborative relationship with law enforcement. This attack may be overt, or it may be suggested in questioning that tries to establish some sort of bias.

As noted above, the expert should answer each question directly and accurately, even if the response will be adverse to the party who presented the witness. That party has the opportunity for redirect examination, a second round of questioning meant to respond to or clarify points raised by or during cross-examination.

However, if a cross-examination question is misleading or cannot be answered with a simple "yes" or "no," there is nothing wrong with the expert carefully stating that "I cannot answer that question with a simple 'yes' or 'no.'"

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