Academic journal article Forensic Science Communications

The Use of Bayes Coefficients to Assess the Racial Bias-Hair Analysis Conjecture for Detection of Cocaine in Hair Samples

Academic journal article Forensic Science Communications

The Use of Bayes Coefficients to Assess the Racial Bias-Hair Analysis Conjecture for Detection of Cocaine in Hair Samples

Article excerpt

Introduction and Background

For more than a decade, the allegation that hair analysis is "racially biased" in the identification of cocaine and its metabolites has persisted in the face of a lack of substantial empirical support. It has been argued, contrary to the bias claim, that assessment of cocaine hair assays based on large data sets has failed to show any significant racial bias when also accounting for self-reported use and when appropriate statistical analysis is done. Yet, in spite of these criticisms and a general rejection by the courts of the claim of race bias in hair analysis, the belief in the racial bias of hair analysis continues to surface.

It is not our intention to revisit in detail the totality of the literature and the series of publications bearing on this topic, which are quite extensive. This has been done elsewhere, and those interested in the history of this controversy are referred to that literature (see Cone and Joseph 1996; Henderson et al. 1993, 1996, 1998; Hoffman 1999; Joseph et al. 1996; Kelly et al. 2000; Kidwell 1996, 1999; Kidwell and Blank 1990, 1991; Mieczkowski 2000, 2001, 2003; Mieczkowski and Kruger 2001, 2007; Mieczkowski and Newel 1993, 1995, 1999; Schwartz 2001; Stepan 1982; Zuckerman 1990).

The race-bias argument has taken two forms: one is based on largely uncontrolled clinical assay outcomes in which African Americans have been reported to test positive for cocaine more frequently than Caucasians in several small N studies. An analysis of those studies, we believe, calls into question any conclusions relating hair analysis to racial bias. The second basis for this argument is derived from laboratory animal studies in which black-pigmented animal fur has been found to retain cocaine at higher concentrations than nonpigmented fur. These studies, using mainly guinea pigs and rats, have suggested, by inference, that "dark-haired persons" may retain more cocaine in their hair than "light-haired persons," and therefore by further inference, that African Americans, being largely dark-haired, would be more likely to test positive for cocaine. Hence the conclusion deduced from this chain of premises is that the test is "biased."

We have taken issue with this conclusion on several different levels. Our response to the reported bias findings has included the following arguments:

1. There is no scientific consensus on the biological meaning of the terms used to describe race as applied to humans or even what aspects of race, if any, have a biological component. There are important sociological definitions, certainly, but the systematic biological dimensions attached to race, if any, are largely unknown.

2. If such a biological dimension existed, it is unknown how these putative "racial characteristics" such as hair and dermal pigmentation are distributed. Not having knowledge of the differential distribution of these traits precludes any generalizations about racial difference. In spite of this, the concept of racial identity has been treated as though it were a well-defined set of biological attributes whose distribution is well documented. Also, within the analytic framework of these studies, race has been treated as an exclusive and exhaustive property--an assumption that is clearly erroneous (e.g., see Henderson et al. 1998).

3. On the preanalytic side of this issue, across these studies, there is no uniformity in the protocols for preparing hair samples, making the results largely noncomparable because they use very different preparatory methods.

4. The subjects constituting the samples in these studies are, at best, convenience samples. No attempt has been made to evaluate the race hypothesis with a view to the problem of generalization, although these studies have readily suggested generalized conclusions--in some cases, rather extreme ones. We note as well that the statistical procedures used, when they have been used, are often inappropriate given the data. …

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