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Law 101: Legal Guide for the Forensic Expert

Response to Claims of "Junk Science"

Response to Claims of "Junk Science"
National Institute of Justice (NIJ) (see reuse policy).

The catchphrase "junk science" has been popularized to describe situations in which the testifying expert, or the expert's testimony and conclusions, is considered or found questionable due to an allegedly poor or insufficient scientific foundation. The testifying expert should be aware that cross-examiners may pursue some of the following lines of questioning in an attempt to challenge a supposedly inadequate, incompetent or unprofessional forensic witness.


  • Showing that the witness is not very knowledgeable on the subject.

  • Exposing a lack of meticulous attention to detail that the expert witness failed to follow in preparation.

  • Cross-examining the expert as to lack of activity in the professional field, particularly with regard to current education and training, and lack of appropriate seminar and workshop attendance.

  • Avoiding acceptance of the "charlatan" as an expert whenever possible.

  • Establishing that the witness has never testified to the same effect previously, which can be damning during cross-examination.

  • Establishing that the findings of the testifying witness are not consistent with studies of others, thereby eroding the credibility of the witness.

  • Suggesting that the expert's findings often lead to erroneous results, which again jeopardizes the expert's credibility.

  • Often an expert will indicate that present methods are positively related to prior methodology. If that linkage and connection can be dispelled, the weight of testimony and credibility of the witness are threatened.

  • The witness should be pressed for literature that tends to support the testimony. Absence of such literature bolsters the claim of lack of competence and credibility.

  • If tests or examinations conducted by the forensic expert have never been admitted as evidence in a court or other dispute resolution process, this can bring the validity of the extant testimony into question.

  • The aggressive cross-examiner will often show that there is no government regulation or statutory support for the expert testimony, or show that the expert testimony is not approved by the scientific community nor by any government-sponsored methodology.

  • If the cross-examining attorney can establish that the scientific, technical or professional community does not rely on the same tests, procedures or techniques followed by the expert, the expert witness's testimony is seriously eroded.

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