Attorneys and judges involved in custody litigation frequently rely upon the reports and testimony of forensic evaluators. Unfortunately, not all evaluations are reliable. Any number of dynamics can diminish or destroy the reliability of forensic work-product. One of the most pervasive and pernicious of these is bias. To be informed consumers of forensic work-product, lawyers and judges need to understand the insidious nature of bias in its many forms and must know how to identify it in reports and testimony. Additionally, attorneys need to develop trial strategies that will expose bias, which is often hidden beneath the surface of the report, so that the trier of fact can see it plainly and appreciate its insidious impact on forensic reliability.

This article will address the nature of bias and discuss why it is so prevalent in the custody setting. Ensuing articles will deal with the challenges of identifying it in forensic evaluations and exposing it in the courtroom.

Bias as a Mode of Impeachment

Attacking the credibility of a witness by showing that he or she is biased is a well-entrenched method of impeachment. As Wigmore noted, “a partiality of mind is therefore always relevant as discrediting the witness and affecting the weight of his testimony.” Wigmore on Evidence, Chadbourne Revision, Section 940 (Aspen 1970). Bias is so central to credibility that it is deemed “non-collateral,” meaning that the cross-examiner is not bound by the witness's denial of the impeaching question and may introduce extrinsic evidence to prove the bias. Id., Section 948.