Context Effects and Observer Bias—Implications for Forensic Odontology

Mark Page,1 B.D.Sc. (Hons), Grad.Dip.Clin.Dent., G.C.Ed.; Jane Taylor,1 B.D.S., B.Sc.Dent., M.D.Sc., Ph.D.;
and Matt Blenkin,1 B.D.Sc., M.Sc.Dent.
J Forensic Sci, 2011
doi: 10.1111/j.1556-4029.2011.01903.x
Available online at:

ABSTRACT: Psychologists have long recognized the effects of contextual and extraneous information on decision making. Such information renders the subject susceptible to both motivational and cognitive bias; yet, it is difficult to assess the extent to which these influence forensic odontologists opinions as there have been no studies to date on this subject. This article explores the various types of contextual effects and biasing influences that potentially impact on the analysis of bitemarks in forensic odontology. It appears that the current practice of bitemark analysis is rich in sources of potentially biasing influences. In addition to the fundamental recognition that some form of bias is likely to exist, ways in which these should be minimized include: separation of the collection and analysis phases; limiting the amount of contextual information available to the odontologist responsible for the analysis; and ensuring that evidence that is ambiguous or of poor quality is identified as such prior to analysis.


Bitemark Certification Board Objects to Defense Subpoena Demanding Release of Expert Opinions

By Dr. Michael Bowers

Recently, in the District of Columbia Superior Court, the forensic organization that certifies bitemark analysis made a failed attempt to suppress expert opinion in a bitemark case. The case in point is US v Ridley, a recently tried murder case involving a human bitemark on the deceased victim. Preceding the trial, there was oral argument over the admissibility of expert reports unfavorable to the District’s prosecution theory of the defendant’s guilt.

The prosecution’s expert, who is an ABFO certified forensic dentist, used the photographs of the victim’s bitemark and the defendant’s dental models as the bitemark testing material for the 2011 ABFO certification exam. That’s a error because the case had not been tried, nor a verdict determined at the time of the ABFO exam. The legal crux of this matter is simple. Each board certification applicant who took the ABFO exam completed a detailed analysis of the Ridley evidence, wrote extensive reports for the ABFO testing committee, and gave oral presentation of their findings. The defense counsel argued in court its legal right to see these reports. A subpoena for these heretofore-unknown reports was submitted by the defense and placed before the judge. The prosecution objected and a hearing was then held, which is the source of this post’s information.

The prosecutor in this case who responded to the subpoena, spoke to the judge and represented the prosecution’s and the ABFO’s objections to the release of these reports. Evidently the reports submitted for board certification were contrary to the prosecutions expert. In a real science if the prosecution’s dental expert made a mistake and published the bitemark evidence (only photos and dental models; no other documentation from the case were included and teeth models of a second fictitious suspect were included for the exam), then the forensic group should admit to the error and agree to the legal right of the court and the defendant to examine the additional reports written by board eligible dentists, who are all now board certified dentists.

The judge heard both sides, and in telephone testimony from the prosecutor’s expert confirmed that these extra judicial reports existed. In a surprise revelation, most or all of the reports did not concur with either the prosecutorial dentist’s opinion or the reports from the two additional dentists who rendered second opinions on the behalf of the prosecution’s dentist. Subsequent to these revelations, the judge granted the subpoena and ordered the ABFO to produce all reports and materials germane of the four applicants.

In a communication to the defense counsel in a last ditch effort to minimize the impact of the findings, the two past ABFO presidents who were tasked with obtaining and divulging the exam reports and evidence, commiserated once more on their objections to the subpoena. Their reasoning, in part, is this statement:

The candidates were required to show how their opinions were formed and evaluated on their ability to present the facts of the constructed case, communicate and demonstrate their analysis methods, and defend their conclusions.

Again, this was a created and fictitious case scenario. No “right” or”wrong” conclusions existed. The candidates were not graded on the absolute “correctness” of their opinions but rather on the processes they utilized to reach those conclusions.

There was no intent or attempt to make this examination scenario identical or similar to any existing actual casework.

Understanding actual bitemark cases and the use of limited information about a patterned injury in skin as a board examination are vastly different. Thus, it is not appropriate to compare the two processes.

Now, am I missing something here? The physical evidence materials for the ABFO bitemark exam were taken from an actual case that had not been tried yet. The use of a case’s extraneous documentation and circumstantial information should be withheld from a forensic examiner (fingerprint, firearms, DNA to name a few) until after the physical analysis is complete. Yet the ABFO appears to differ with this protocol and clearly state that all this extra information is necessary to render a final opinion on the analysis of physical evidence. Therefore, the ABFO bitemark exam is not representative of actual casework or the practice of bitemark identification.

How vastly different is forming an opinion on limited information on a patterned injury in skin from forming an opinion in an actual case? This was material from an actual case. If it is not appropriate to compare the processes, then what benefit does the ABFO applicant gain by completing the examination? If all that is important is following a process to form an opinion, and the correctness of the answer is unimportant, then what value is ABFO certification for the trier of fact?

Does the Forensic Science Advisory Board of the American Academy of Forensic Science know about this? This is the parent organization that certifies the ABFO. I t certainly should, because one of the ABFO past presidents who wrote the above quote is Secretary of the FSAB. The FSAB might also like to know that the results of the examination were destroyed, against the standards of the FSAB.

So the much embattled American Board of Forensic Odontology (ABFO), continues its uphill fight to preserve its courtroom credibility by offering direct support for the continued prosecutorial use of their Congressionally debunked and scientifically untested bitemark comparison opinions. The ABFO continues to orchestrate its membership down the unacceptable path of prosecutorial partisanship.