biases in forensic science procedures,2 but much more must be done to understand the sources of bias and to develop countermeasures.3 Some principles employed in other fields should be useful, although some (e.g., blinding) may not be feasible for some types of forensics work. The forensic science disciplines are just beginning to become aware of contextual bias and the dangers it poses. The traps created by such biases can be very subtle, and typically one is not aware that his or her judgment is being affected. An overview of the effect of bias in the forensic science disciplines can be found in Risinger et al., 2002.4 Decisions regarding what analyses need to be performed and in what order also can be influenced by bias and ultimately have the potential to skew results.

Forensic scientists who sit administratively in law enforcement agencies or prosecutors’ offices, or who are hired by those units, are subject to a general risk of bias. Bias also is introduced through decisions made about evidence collection, which controls who is listed as a suspect. Evidence collection and crime scene investigation can require scientific knowledge and judgment, and these functions are normally outside the control of forensic scientists.


There is a critical need in most fields of forensic science to raise the standards for reporting and testifying about the results of investigations. For example, many terms are used by forensic examiners in reports and in court testimony to describe findings, conclusions, and the degrees of association between evidentiary material (e.g., hairs, fingerprints, fibers) and particular people or objects. Such terms include but are not limited to “match,” “consistent with,” “identical,” “similar in all respects tested,” and “cannot be excluded as the source of.” The use of such terms can have a profound effect on how the trier of fact in a criminal or civil matter perceives and evaluates evidence. Yet the forensic science disciplines have not reached agreement or consensus on the precise meaning of any of these


E.g., I.E. Dror and D. Charlton. 2006. Why experts make errors. Journal of Forensic Identification 56 (4):600-616; I.E. Dror, D. Charlton, and A Peron. 2006. Contextual information renders experts vulnerable to making erroneous identifications. Forensic Science International 156(1):74-78; D.E. Krane, S. Ford, J.R. Gilder, K. Inman, A. Jamieson, R. Koppl, I.L. Kornfield, D.M. Risinger, N. Rudin, M.S. Taylor, and W.C Thompson. 2008. Sequential unmasking: A means of minimizing observer effects in forensic DNA interpretation. Journal of Forensic Sciences 53(4):1006-1007; L.S. Miller. 1987. Procedural bias in forensic science examinations of human hairs. Law and Human Behavior 11(2):157-163.


See the discussion of biases provided in Chapter 4.


D.M. Risinger, M.J. Saks, W.C. Thompson, and R. Rosenthal. 2002. The Daubert/Kumho implications of observer effects in forensic science: Hidden problems of expectation and suggestion. California Law Review 90:1-56; Krane, et al., op. cit.

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