Abstract

 

Commentators in
the legal community have expressed concerns that forensic microscopical hair
comparisons may not be scientific and may not meet admissibility criteria set
forth in the Federal Rules of Evidence and guiding legal decisions. Forensic microscopical
hair comparisons are founded on the precepts of comparative biology,
microscopy, zoology, histology, and anthropology. Empirical testing
demonstrates that, while not absolute positive identification, hair comparisons
are good evidence of association. The validity and acceptance of forensic hair
comparisons are supported by guidelines for hair comparison methodology, papers
in peer-reviewed journals, textbooks, and specialized training schools. Hair
comparisons are a service offered by both public and private forensic science
laboratories. Hair comparison testimony has been accepted in local, state and
federal courts for decades. In the authors’ opinion, forensic hair comparisons
meet every criteria required by the Federal Rules of Evidence, Frye, and
Daubert.

 

Introduction

A few legal commentators have revived old arguments
about certain fields in forensic science in light of the Daubert
decision, based on sparse legal rulings (Williamson v. Reynolds, 1995),
legal publications (Rudolf, 1996; Saks, 1993; Smith and Goodman, 1996),
and discussion among lawyers and forensic scientists (AAFS, Joint Session,
1996). Particularly, they are attentive to the concern that hair comparisons
may not be scientific and thereby not meet the Daubert criteria.
Similar challenges have recently been launched against forensic document
examiners and fingerprint examiners. In the most serious challenges
to date, courts have ruled that forensic document examination was not
scientific and did not have to meet the Daubert standard; it
was, however, admissible as expert witness opinion testimony (U.S. v.
Starzecpyzel, 1995; U.S. v. Jones, 1997).

Forensic hair
comparisons, however, meet the criteria required by the Federal Rules of
Evidence (FRE 702) and both Daubert and its predecessor, Frye.
Hair comparison testimony has been accepted in local, state, and Federal courts
regularly for decades (U.S. v. Haskins, 1976; U.S. v. Cyphers, 1977; U.s. v.
Brown, 1977; State v. Watley, 1989; State v. Faricloth, 1990; State v. Payne,
1991; State v. Bridges, 1992; Crawford v. State, 1992; People v. Wettese, 1992;
Suggs v. State, 1995; McCary v. State, 1995; Beam v. State, 1995; U.S. v.
Matta-Ballesteros, 1995). The confusion and misunderstanding by the legal community
stems from a variety of sources, including popular notions about science in
general and specifically forensic science, using forensic DNA examinations as a
model for interpreting forensic hair examination results, and the difference
between calculating probabilities and scientific reliability. Coupled with
results that offer a range of certainty about the conclusions and an incomplete
knowledge about forensic hair comparisons by the non-scientific members of the
legal system and non-forensic scientists, this misunderstanding has led to
isolated instances of hair comparison evidence being ruled inadmissible
(Williamson v. Reynolds, 1995; McGrew v. State, 1996). Considering the relevant
issues and the recent attacks, the authors think hair evidence should survive
and remain a useful part of criminal investigations and trials. This is not
only because forensic hair comparisons meet the requirements of FRE 702, Frye
and Daubert, but primarily because they are a sound and useful forensic
science.

The Science of Forensic Hair Comparisons

Forensic hair
examinations are a comparative biological discipline grounded in the most basic
ideas of microscopy, biology, anatomy, histology, and anthropology. The
phenotypic characteristics of human hairs are assessed by observing the
microscopic anatomy of a hair and estimating the body area, racial
characteristics, disease effects, post-mortem effects, and trauma. The
microscopic anatomy of hairs from representative samples is detailed and
characterized based on its histological traits, such as the cuticle, medulla,
cortex, pigment granules, cortical fusi, and others (Figure 1). The
distribution and arrangement of these traits is important to the description of
a hair or hairs.

Histology, the study of basic tissues and the microscopic
anatomy of the body, is an excellent analogy to forensic hair comparisons
(Ham, 1974). Histologists and pathologists identify tissue and cell
types, cell anomalies, and other traits by their microscopic appearance.

 


Figure 1.
Phenotypic
traits of human hairs (list not inclusive of all traits)

Their identification of a cancerous cell does not turn
on a probability; no statistic is calculated to determine the likelihood
that a cell is either a neuron or a liver cell. It is visual identification
based on known characteristics and comparison with known type samples.
Likewise, forensic scientists visually identify human and animal hairs
and determine body area origin, racial characteristics, and microscopic
anatomy. Forensic hair examiners also compare questioned hairs to known
hair samples to assess microscopic similarity. The growth and biology
of hair as a part of the epithelial tissue comes under the disciplines
of embryology and histology.

What, and How, Is Science?

The science of
forensic hair comparisons, like all science, is a means of asking and answering
questions. The methodology of science has been widely published both for
scientists and non-scientists (Poundstone, 1988) and will be reiterated here
only briefly. People often ask questions about the same subjects scientists
themselves question, but they use different methods to answer them. Science, on
the other hand, bases its existence on the possibility of alternative
explanations and the ability to replace one theory with another. In that vein,
science has a number of objectives as outlined by Ayala (1969):

 

    1. The systematic organization of
      knowledge to facilitate the discovery of relationships and
      patterns among
      phenomena and processes,

    1. The explanation for the
      occurrence of these phenomena and processes, and

  1. The proposal of these
    explanations in a format which is open to the possibility of rejection.

 

Forensic hair
comparisons comply with each of these objectives. After a systematic collection
and description of the physical evidence, in every case, the study begins as a
tentative, working statement, called a hypothesis, and advances either to
demonstrated disproof and rejection or to continuing support and acceptance. A
hypothesis is a testable statement in science; it is either rejected or
supported. Hypotheses are either descriptive or explanatory. A descriptive
hypothesis is a statement of asserted fact. It may be true or false but it
still does not explain anything: Saying it was 95o yesterday does
not explain why it was that hot or that birds are migratory does not propose
the underlying mechanisms of that event. Descriptive hypotheses (facts) are
inherently non-explanatory, which is why no theory ever becomes a fact.

An explanatory
hypothesis, however, does try to explain something. It must be testable, and is
tested indirectly through facts. Explanatory hypotheses are frequently
incomplete because the phenomenon is still under study and is not yet fully
understood. This does not mean that an incomplete hypothesis is false and
worthless. Most scientific hypotheses are ultimately incomplete because the
fields from which they arise are still being explored. Hypotheses that are
accepted today are accepted because they are supported by current knowledge and
what accounts for that evidence. To criticize a hypothesis for being incomplete
or not totally proven is to reveal ignorance about the nature of the scientific
method. Only facts are directly verified: Theories never are.

Science, as a
discipline, can be distinguished from other ways of knowing, such as religion
or common sense, by two distinct characteristics: (1) the manner in which
science establishes the correctness of conclusions, and (2) the integration of
those conclusions into a systematic body of knowledge (Dunnell, 1982).
Scientists apply a number of principles in the assessment of conclusions (e.g.,
symmetry, parsimony, coherence, correlation) but as Dunnell states,

“…the
ultimate arbitrator is comprised by…’performance criteria’, i.e., how well a
proposition works in an empirical context…The use of performance criteria
permits definitive experimentation and definitive empirical testing. Scientific
propositions must have definitive empirical consequences.” (1978: 199)

Generally
accepted procedures and performance criteria have been established for forensic
hair comparison (for example, see Proceedings of the International Hair
Symposium, 1985). It is the testability of these published performance criteria
that allow forensic scientists to assess the accuracy and precision of
techniques applied, based on a particular theory, and used for a specific
purpose, like hair comparisons.

The Tyranny of Numbers: Not All Science Is Physics

Much of the
history of science is rooted in the ancient traditions of Greece, Rome, and the Middle East. The Greek philosophers, including Aristotle, were
primarily rationalists, a branch of philosophy that posits the solutions to
scientific problems simply by focused reasoning, involving what we would now
call deduction. Historically, the success which these ancient scholars had in
their explanations led to “an overrating of a purely rational
approach” (Mayr, 1982) that culminated with the French philosopher and
mathematician Renee Descartes. Descartes believed the most scientific
conclusions and theories were those that had the certainty of a mathematical
proof. This idea exists even today, particularly in the popular concept of
science. It has persevered not only in the physical sciences, where
mathematical proofs are often possible, but also in the biological sciences
(Mayr, 1982). This tyranny of numbers obscures the potential many disciplines
have of achieving an optimal level of resolution because a mathematical value
is expected but may not be possible (Houck, 1999). In many cases, it may be
impossible for biologists to provide proofs of pure mathematical certainty due
to the complex nature of living systems.

 

The other way of
approaching reasoning is induction, where we build up observations and
generalize about the world from them (Poundstone, 1988). Common sense and much
of what we know about the world comes from our essentially inductionist
approach to life and learning. As Poundstone describes it,

You see a raven. It’s
black. You see other ravens, and they’re black too. Never do you see a
raven that isn’t black. It is inductive reasoning to conclude that “all
ravens are black.” (1988:14)

 

Induction is
reasoning from “circumstantial evidence”, not at all uncommon in
litigation, and it expands our knowledge of the world.

 

Which is more
appropriate to the forensic hair comparison, deduction or induction? Although
useful to the investigation, deduction alone is insufficient, just as facts
alone are not explanatory. Induction provides the platform, the
“real-world” units (“ravens”) and generalizations
(“all of them [so far] are black”) that allow scientists to identify
and construct deductive, testable arguments. To summarize a hair comparison by
stating only that “the questioned and known hairs exhibit the same microscopic
characteristics” with no interpretation is not useful to the trier of fact.
This deductionist approach is only half of the picture. The results should then
be put into a meaningful context, usually through induction: “And, accordingly,
they could have come from the same original source.” The examiner comes to this
conclusion based upon his or her experience, training, and laboratory protocols
in hair comparisons.

In essence,
deduction and induction constitute the scientific method applicable to hairs.
The basics of biology provides the larger scientific context and the units of
observation; the legal application of biology, whether DNA or microscopic hair
comparisons, is merely one aspect of the greater process of science as a tool
for understanding the world around us. These observations are made within a
mental framework of theory that predetermines the structure into which they fit
and against which they are tested. Theory drives observation, observation yields
facts, and facts build and adjust theory.

The tyranny of numbers is a consequence of an over-reliance
on deduction and mathematics that ultimately cheat a discipline; it
could also be called “physics envy.” Equating quantification with science
in an attempt to justify and validate its “science-ness” indicates
that a faulty notion of science, or no notion at all, is at the heart
of the tyranny (May, 1982). Additionally, some information simply does
not lend itself to a mathematical approach. Historical certainty, for
example, is different from, but not inferior to, mathematical certainty
(Cleland, 2001). The existence of trilobites, dinosaurs, the cave paintings
at Lascoux, and the Roman Empire are as certain as anything in mathematics
but cannot be distilled into a formula.

What forensic
scientists do is try to disprove hypotheses. If a hypothesis (e.g., the
questioned hair exhibits the same microscopic characteristics as hairs
composing the known sample) is tested and cannot be disproved, confidence is
gained in it. The more it is tested by more methods and the more they fail to
disprove it, the more confidence is gained that it is valid. In this sense,
there is no such thing as an absolutely true theory or explanation. Something
may come up tomorrow, like new evidence, to require an idea to be rejected;
scientific truth is what we know up to this moment.

 

Simply observing
the world is not enough. The late eighteenth century saw the first application
of a method suitable for the study of diversity: The comparative method. The
disparity between experiment and comparison is actually small. Mayr (1982)
points out that in experimentation and comparison observed data plays a crucial
role. The main difference between the observations is that in an artificial
laboratory experiment, the conditions are chosen and the experimenter is able
to test those specific factors that yield the outcome. Experimentation is often
inapplicable to many biological problems. This does not make the comparative
method inferior to experimentation; the conditions may vary but other controls
can be imposed to provide useful scientific information.

Another factor
adding to the legitimacy of the comparative method is that a side by side
comparison process of detailed observations is different from a person making a
subjective determination of the properties of an object, such as simple
description. This “point-by-point” comparison, as is done with hair
comparisons, is a powerful technique, one that suited biology, taxonomy, and
zoology since it was developed by the French naturalist Georges Cuvier
(1769-1832). Each discipline requires its own appropriate methodologies and the
credibility of the hypotheses generated by a discipline should be evaluated
relative to that discipline’s methods and body of knowledge (Hume, 1934). Just
because the Kreb’s cycle cannot be explained by Heisenberg’s Uncertainty
Principle does not mean it is not based upon a valid theory.

Why
Can’t You Calculate a Probability Like DNA Does?

Clinical studies
(Bisbing and Wolner, 1984; Lamb and Tucker, 1994; Gaudette, 1976; Gaudette and
Keeping, 1974; Strauss, 1983; Wickenheiser and Hepworth, 1990) and individual
observation (experience) demonstrate that forensic hair comparisons also
provide an excellent means of discriminating between individuals. For example,
in 1974 Gaudette and Keeping found that in 366,630 comparisons of brown
Caucasian head hairs, only 9 pairs of hairs were indistinguishable. Similarly,
Wickenheiser and Hepworth (1990), in a related study, found that in 431,985
comparisons of brown Caucasian head hairs, only 6 or 7 pairs were
indistinguishable. Performing comparisons with brown Caucasian pubic hairs, in
101,368 comparisons, only 16 pairs were unable to be distinguished (Gaudette,
1976). In a multiracial study, Strauss (1983) reported that 100% of racial
assessments were correct and no incorrect inclusions or exclusions were made in
4,900 comparisons. In a review of 170 hair cases at the FBI Laboratory, only 9%
of the positive microscopical comparisons were excluded by mitochondrial DNA
testing (Houck and Budowle, 2002). These clinical studies, and others, indicate
that forensic hair comparisons have a scientific validity and basis in
demonstrable fact.

All of these
numbers notwithstanding, to attempt to derive a population frequency of traits
or to determine how likely it may be to encounter a given hair in a given
population is fraught with complexity. Most experts testify that the likelihood
of finding someone else with indistinguishable hair is remote, a rare event
(Bisbing and Wolner, 1984; Lamb and Tucker, 1994; Gaudette, 1976; Gaudette and
Keeping, 1974; Strauss, 1983; Wickenheiser and Hepworth, 1990). They do not
feel comfortable with any statements about the probability that a specific hair
could have come from someone other than the person to which it was associated.
The authors agree with that approach. The justification for that reluctance is
based on the complexity of the probability question, difficulty choosing a
population to which to assign the probability (for example, see Buckleton and
Walsh, 1991), the lack of sufficient data where that question was addressed
(Ogle, 1998), and court decisions excluding such statements of probability in
the past.

Regardless of
the legal community’s interest in a “simple” probability statement, a
statistical calculation that a particular hair, in a particular case, which has
been associated with an exemplar, could have originated from another unknown
random individual is currently impossible. It may be possible to use error
rates, frequencies of specific hair traits in a given population, or likelihood
ratios to illustrate the significance of a hair comparison, but the data for
these values are minimal or anecdotal. Besides, the Daubert decision
requires the error rate for the procedure, and not the examiner per se. The
applicability of a specific error rate (one sample, one examiner) to any one
particular case is doubtful.

“In order
to assess the probability of an incorrect inclusion or incorrect exclusion of a
suspected source for a questioned hair, the examiner must first have frequency
data for the set of varieties (the hair type) which forms the match
constellation” (Ogle, 1998) combined with the likelihood given a whole
host of other contextual facts related to the case at hand. Consider an
example: If two people are riding in the front seats of a car involved in a
head-on crash, the likelihood is very low that the hairs imbedded in the
windshield, which exhibit the same microscopic characteristics as occupant A
but different characteristics as occupant B, came from a third unknown person.
The authors think the hair evidence from such a case would be probative,
assuming its relevance to the lawsuit. The reliability and admissibility is not
measured by knowing the probability that a particular hair could have
originated from another unknown person. Another example: if a questioned hair
was found on a bank floor after a robbery, the likelihood that the hair
originated from an unknown third party seems more important to consider.

In statistics,
accuracy and confidence are inversely related. If the estimate of the number of
coins in someone’s pocket is less than 500, one would have 100% confidence in
that value. It is not, however, optimally accurate and not a very useful
number. Uncertainty is a part of science and is recognized as such by the Daubert
court in requiring error rates: The rate of error must be known but it does not
have to be zero. As discussed previously, however, an over-reliance on strict
statistical certainty reduces a discipline to an inflexible dogmatic approach
instead of science. Additionally, comparison of a qualitative, descriptive
science like hair comparisons with a quantitative method like DNA analysis is
unfounded (Houck, 1999). Forensic hair comparisons deal with the
characterization of continuous phenotypic variation while DNA renders results
based on discrete, quantified genetic information. The two are no more alike in
this respect than calculus and geometry.

Hairs and DNA

The advent of
mitochondrial DNA (mtDNA) sequencing provides an additional test for assessing
source association between a questioned hair and an individual. Neither the
microscopic nor mtDNA analysis alone, or together, enables absolute positive
identification; together, however, these methods can be complementary
examinations. For example, mtDNA typing can often distinguish between hairs
from different sources although they have similar morphological characteristics
(or insufficient characteristics); in contrast, hair morphology comparisons can
often distinguish between samples from different individuals that are
maternally related, where mtDNA analysis is uninformative. Moreover, the
addition of mtDNA analysis provides for the assessment of the performance of
microscopic hair comparisons.

A recent study has shown the utility of performing
microscopic and DNA hair examinations (Houck and Budowle, 2002). The
results of the 170 hair comparisons and subsequent mtDNA sequences were
evaluated. For the microscopic comparisons, 58.2% of the analyses yielded
conclusive results (80 associations and 19 exclusions). Comparatively,
94.7% of the evidence hairs yielded conclusive results by mtDNA sequencing
(97 concordant and 64 exclusions). The greater success for mtDNA typing
compared with microscopic analyses should not be a surprise—many morphological
characteristics in an individual’s hair are expressed as a distribution.
Additionally, mtDNA sequencing is a very sensitive technique that requires
only 1-2 cm of hair and often only a single reference is required for
comparison purposes.

Of the 170 microscopic examinations that were made
in this study, 37 (21.7%) were inconclusive as to association or exclusion
and 34 (20%) were not suitable for examination. However, mtDNA sequencing
provided information for 35 inconclusive and 31 insufficient hairs,
66 in total; this information was exculpatory in slightly more than
half of these “uninformative” hairs. A qualified hair examiner should
still view the hair microscopically to determine its qualities and description.
Mitochondrial DNA analysis is destructive and a photographic record
of the hair should be made prior to submission to the DNA analyst.

Microscopic hair comparisons can exclude samples
where the mtDNA sequences are the same, such maternal relatives or unrelated
people with the same mtDNA sequences; by contrast, hairs that cannot
be excluded due to a congruence of features will also exist. Of the
80 hairs that were microscopically associated, nine comparisons were
excluded by mtDNA analysis. Many of these (4 or 44%) were defined as
blond Caucasian head hairs. Blond hairs, by their coloration, have much
less pigmentation than darker hairs and, because pigmentation is an
important comparison characteristic, hairs with sparse or no pigmentation
but from different sources could appear similar. It must be stressed
that these nine mtDNA exclusions are not a false positive or error rate
for the microscopic method or a false exclusion rate for mtDNA typing.
These results display the limits of the hairs in this sample only and
not for any hairs examined by any particular examiner in any one case.
The microscopic comparison is not an absolute identification and therefore
some small number of individual hairs that have a congruence of certain
characteristics, even though they originate from separate individuals,
may exist. In those rare instances where the same microscopic characteristics
are exhibited in hairs from different individuals, the appropriate interpretation
for the microscopic comparison is association.

There were no apparent differences in the exclusions
obtained with both analytical methods. Of the 19 microscopic exclusions,
17 were confirmed by mtDNA sequencing. The other 2 hairs provided inconclusive
or insufficient results with mtDNA sequencing: The exculpatory power
of hair comparisons appears to be quite good. It therefore seems reasonable
to continue to routinely examine hairs microscopically because a microscopical
comparison can reliably exclude hairs, which is a principle aim of the
forensic comparison. When the hairs are not excluded, the power and
complementary value of mtDNA can be exploited.

The
Admissibility of Hair Comparison Evidence

The
admissibility of hair comparison evidence will depend to a slight extent on
which rule is applicable and the interest by the trial judge in being a
gate-keeper. Any problems with admitting hair evidence can partly be solved if
the trial court is educated better by forensic scientists to the methodology
and reliability of hair comparison science. Forensic hair comparison evidence
fits the requirements of science and the rules of admissibility including Frye
and Daubert.

 

Why
Do Forensic Hair Comparisons Pass the Frye Test?

While Frye
(U.S. v. Frye, 1923) is based on general acceptance in the scientific
community, which occasionally has been difficult to define (Green, 1992;
Thornton, 1994), it is still used by many jurisdictions in the United States. The microscopic examination of hair using the comparison microscope has been
the accepted standard technique for the examination and comparison of hairs for
approximately the past 60 years, and, as such, this technique has been accepted
by both State and Federal courts throughout the United States, in all U.S.
Territories, Canada and in many European and Asian countries.

The Frye
standard usually involves a two-point question: Is the field in which the
underlying theory falls generally accepted in the relevant scientific
community?
For hair comparisons, the answer is “yes.” Comparative biology,
including medicine and physical anthropology, has a long history of microscopic
identification and comparison dating back to the 18th century. Comparison is
the cornerstone of the majority of biology, both past and present. Microscopic
techniques, combined with studied experience, provide for a highly
discriminating means to examine and compare hair (Bisbing, 1982). A long
history of research in physical anthropology and forensic science detailing the
differences between peoples’ hair supports the credibility of the relevant
science (Bisbing, 1982; Hausman, 1925a; 1925b; Hausman, 1928; Houck, 2001;
Kirk, 1994; Trotter, 1930; Trotter, 1938).

The reliability
of the identification and association of human hair, assuming a competent
comparison, is based on extensive experience by forensic laboratories around
the world since about 1932, including the FBI, Royal Canadian Mounted Police,
state, and local forensic laboratories, as well as private laboratories and a
body of peer reviewed scientific literature.

Forensic hair
comparison has a generally accepted theory and basis for a reliable scientific
practice, based on literature in the Journal of Forensic Sciences, the Journal
of the Forensic Science Society
(now Science and Justice), the Canadian
Society of Forensic Science Journal
and other related peer-reviewed
scientific journals and publications, forensic science textbooks (for example,
Saferstein, 1996), and technical reference books (for example, Saferstein,
1982) used by forensic scientists. State and Federal forensic science agencies,
university forensic science programs, and private research institutes regularly
hold specialized training courses that teach hair comparison theory and
methodology (Proceedings of the International Symposium on Forensic Hair
Comparisons, 1985). An extensive body of literature exists for hair biology and
comparisons (Houck, 2001).

There is also a
collection of court decisions from all over the country where hair evidence has
been admitted over objection and upheld on appeal. Numerous case precedents
exist for admissibility of forensic hair examinations as a valid and reliable
science (U.S. v. Haskins, 1976; U.S. v. Cyphers, 1977; U.S. v. Brown, 1977;
State v. Watley, 1989; State v. Faricloth, 1990; State v. Payne, 1991; State v.
Bridges, 1992; Crawford v. State, 1992; People v. Wettese, 1992; Suggs v.
State, 1995; McCary v. State, 1995; Beam v. State, 1995; U.S. v.
Matta-Ballesteros, 1995).

Are there
procedures available that can produce reliable results and are they generally
accepted in the relevant scientific community?
Specific techniques for hair comparisons
do exist based on previously cited literature, the curriculum of the courses
taught, the protocols that exist in most forensic science laboratories,
specifically those that are accredited or are undergoing accreditation, and the
experience of two generations of forensic scientists. Hair comparison tests can
be constructed to have discrete answers and are, therefore, testable. Forensic
hair examiners undergo testing during training and many take proficiency tests
once qualified (Peterson and Markham, 1995a, 1995b).

Several clinical
studies and research projects with published and peer reviewed reports have
demonstrated that given a limited number of questioned and known hair samples,
correct inclusions and exclusions are the rule rather than the exception
(Bisbing and Wolner, 1984; Lamb and Tucker, 1994; Gaudette, 1976; Gaudette and
Keeping, 1974; Strauss, 1983; Wickenheiser and Hepworth, 1990).

Why
Do Hair Comparisons Also Pass the Daubert Test?

Daubert (Daubert v. Merrell Dow, 1993),
by comparison with Frye, has a four-pointed definition of admissibility:
No single point must dictate the outcome of the Daubert scrutiny but any
single point may dictate the outcome. For example, a reviewing court may decide
that, because a forensic discipline has gained general acceptance, it will be
admitted. Daubert’s four main points are as follows.

1. Can the
procedure be tested and thereby validated?
As mentioned in the Frye discussion, hair comparison
procedures can be tested by controlled research and proficiency testing. The
fact that when two hair samples are randomly selected from the population and
compared microscopically, it is very unusual that they cannot be distinguished
(Hicks, 1977) has been borne out by the previously cited clinical trials. In
individual cases, the associations can be tested by re-analysis by another
qualified examiner (peer reviewed).

2. Is the
procedure peer reviewed?

There is a wealth of peer reviewed literature regarding hair characteristics,
variation between individuals, forensic hair comparison techniques, and
reliability studies. Additionally, although perhaps not what the Supreme Court
had in mind, many laboratories employ a peer review or confirmation process
whereby the hair examiner, having determined that questioned hairs from items
of evidence and known hair standards exhibit the same microscopic
characteristics, then takes these hairs to another qualified examiner. This
second hair examiner reviews the hairs microscopically, employing the same
methodology as the first hair examiner. The second examiner is free to agree or
disagree with the first examiner’s results. Only when both examiners agree is
the hair association reported. The advent of mitochondrial DNA testing
(Budowle, et al., 1990; Wilson, et al., 1993; Wilson, et al., 1995a, 1995b) of
hair provides another test, one based on strictly genetic information.
Mitochondrial DNA sequencing in itself does not provide absolute positive
identification but when combined with a microscopic hair comparison can yield a
very strong conclusion of association.

3. Is the
rate of error for that procedure available?
The rate of error for hair comparisons is contingent upon
the quality, calibration, and maintenance of the microscopes, the training and
experience of the examiner and the quality of the known and questioned hair
samples. Error rates have been reported in the previously cited clinical
trials. Although these reports measurably increase our understanding of error
rates, these rates can only be used as examples or touch points and cannot be
used to predict the probability of error for the case at hand. As with any
application of statistics, the error rate calculation, per se, is a known
quantity based on mathematics; the actual error values depend on the sample
data. If you change the data, you change the error values.

While
proficiency testing can be a valuable training device for reducing errors, “it
is exceedingly difficult to estimate relevant error rates from either
industry-wide or laboratory-specific proficiency-test results” (Committee on
DNA Forensic Science, 1996). However, one study of published proficiency test
results indicates that over a 13-year period, forensic hair examiners erred in
proficiency tests only 8% of the time (Peterson and Markham, 1995a, 1995b). It
should be noted that production of hair proficiency tests is problematic simply
because of the natural variation that human hairs exhibit: Providing
mass-produced, uniform hair samples to many laboratories is just not feasible.
In general, proficiency tests do not mimic actual cases. Every case is
different with different samples, different questions, and different solutions
to the problems at hand, making objective testing of the error rates for
individual cases impossible. This difficulty, however, does not preclude the
validation of forensic hair comparisons but the traditional large-scale testing
of it as employed with other types of evidence.

The error rate
at issue is the error rate of the procedure, not of the person performing the
procedure. If the forensic procedure were one that totally consumed the
evidence at issue, knowing the error rate of the procedure might be necessary
to ensure a defendant receives a fair trial. If the evidence is not consumed or
altered, and is available for review by a defense expert, the prerequisite of
having an established error rate is less necessary.

Daubert requires that the method be reliable, not
absolute. The record needs to reflect why hair comparisons are reliable. For
example, the relevant scientific community has experienced and demonstrated
that it is a rare event that the hair from two individuals cannot be
differentiated microscopically. Additionally, the published clinical trials
indicate that false positives are very rare; false exclusions are by comparison
more common and this works to the defendant’s favor. Daubert, we think,
does not state that the error rates must be zero, only that they must be
understood.

4. Is the
procedure generally accepted in the scientific community?
Since hair comparisons meet this
requirement of the Frye standard, they likewise meet Daubert test
for the same reasons.

When forensic
evidence is introduced in a legal proceeding, it is offered to bolster one of
the parties’ arguments. It should be no surprise then, that legal commentators,
often with an agenda, will seek to exploit isolated, anecdotal legal opinions
to support their argument (for example, see Starrs, 1997).

 One opinion
frequently cited to suggest recent, successful challenges to hair comparison
testimony is State v. McGrew. However, the Indiana Supreme Court subsequently
reversed the lower court’s ruling, and found that the hair comparison testimony
was properly admitted (Williamson v. Ward, 1997). The other similar opinion is
Williamson v. Oklahoma. Appellate review of that portion of the opinion
rejected the criticisms of hair comparison testimony because the review was
conducted under the wrong legal standard (State v. Fukusaku, 1997). Other
jurisdictions have since found that hair comparison testimony is admissible. At
present, there are no recent legal opinions that agree with the views expressed
in the earlier McGrew and Williamson decisions.

Conclusions

Forensic
examinations of human hairs have been performed for years. Depending on the
microscopist’s training and experience, and the condition of the evidence, the
potential rate of error of the technique is very low. The techniques are not
novel and there exists a body of literature dealing with human hair
characteristics and the reliability of forensic hair comparisons. It is true
that hair comparisons, as do all other sciences, depend on the judgement and
experience of the examiner; but hair examiners are scientists and not simply
technicians. That is why they can reliably make the necessary value judgements
that come from their scientific education, training, and experience.

Professional
standards for the practice of forensic hair comparisons have been proffered
through international cooperation supported by international symposia. Like
other forensic techniques, such as firearms, fingerprints and handwriting
comparisons, the forensic comparison of hair has been well-established in the
forensic laboratories of the world. Quality assurance safeguards are in place
in most forensic laboratories which make use of specialized training,
proficiency testing and peer review. The finding of the same microscopic
characteristics in the questioned hair as in the known sample is objective and
demonstrable to the trier of fact; the nature and breadth of the inferences
adduced can be explained easily by the qualified expert. If warranted, experts
are available to re-evaluate the evidence because the method is
non-destructive. If the hair evidence is considered important and valued, a
careful microscopic examination will provide evidence that is reliable and
probative in a criminal investigation and lawsuit. The forensic scientist
should welcome the trial judge’s gatekeeper role and be able to explain the
acceptability of the forensic hair comparison in detail.

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