Capillary Electrophoresis and Daubert:
Time for Admission
The recent telecast of the O. J. Simpson trial has brought to the forefront the importance of forensic identification in legal proceedings, especially in criminal cases. Forensic science has become a key element in proving a defendant's guilt or innocence. In the O. J. Simpson trial, the question was not one of the admissibility of the expert testimony regarding the existing DNA testing procedure and the resulting conclusions, but rather what weight the jury would give these results.
The Federal Rules of Evidence, which are standardized and binding on all U.S. District Courts, are applied to offers of evidence, including testimony, to ensure that juries hear and ultimately consider only admissible material and relevant evidence when deciding issues in a lawsuit. These rules have evolved over the years as courts decide on a case-by-case basis what is or isn't admissible evidence.
According to Rule 401, in order for anything to be admitted into evidence in court it must be relevant. It must assist the trier of fact in that it proves or disproves a matter at issue. In some cases, even if the evidence is relevant, Rule 403 may exclude it if the prejudice against the opposing party outweighs the probative value of the evidence sought to be admitted. Alternatively, evidence may be excluded if it confuses the issues, misleads the jury, or causes undue delay.
According to our research, CE has not been discussed as admissible expert opinion testimony in any reported case. Thus, we believe that when CE is offered at trial, it will be accepted as admissible evidence for the jury's consideration. In this article we address admissible evidence via expert testimony involving a new science. Our hope is to add to the fund of learning and still any fear a scientist may harbor when called to testify as an expert.
Admissibility of scientific evidence: The Frye rule
Before 1993, the standard for determining the admissibility of scientific
evidence was established in Frye v. United States, which held that
"scientific evidence is admissible if it is based on a scientific technique
generally accepted as reliable within the scientific community." Under the
Frye standard, the court was required to review the testimony given at
a Frye hearing, other judicial decisions, the scientific literature,
and relevant legal commentary to determine whether there was "general
acceptance" among scientists in the relevant fields of the proposed
scientific technique or testimony (1).
A technique was not admissible in court if there was a substantial controversy among reputable scientists. Frye did not ask judges to make a judgment on the scientific merits of a controversy; instead, they had to determine whether substantial controversy existed. The Frye analysis began and ended with the same question: Is the scientific technique at issue generally accepted by the appropriate community of scientists?
Initially, the Frye analysis appeared to be a simple one-step analysis of scientific methods. However, it failed to look at the validity of the scientific methods offered, thereby creating a greater chance of admitting "junk science" into court. This analysis failed to recognize that although a novel scientific method may not be generally accepted within its own scientific community, this alone would not necessarily make the method invalid or unreliable. Thus, valid and reliable novel scientific methods could not possibly have stood the Frye test. The Frye analysis did not address the validity of the scientific method, it failed to weed out erroneous scientific methods, and it admitted invalid evidence into courts of law.
A new rule of evidence
In 1992, Congress enacted Rule 702, which states, "If scientific, technical,
or other specialized knowledge will assist the trier of fact to understand
the evidence or to determine a fact in issue, a witness qualified as an
expert by knowledge, skill, experience, training, or education may testify
thereto in the form of an opinion or otherwise." The intent of the rule was
to increase receptivity to experts. If there was any limit to the trial
judge's discretion, it may have been mainly a limit on discretion to
exclude.
In holding that the proper standard for admissibility is governed by the Federal Rules of Evidence rather than by the Frye test, the Supreme Court held that for expert testimony to be admitted, the method of analysis used by the expert need not have gained general acceptance as was required under the Frye test. Instead, Rule 702 consists of three major requirements: the witness must be an expert; the expert must testify to scientific, technical, or specialized knowledge; and the expert must assist the trier of fact or "fit requirement." That is, there must be a valid connection between the expertise in question and the inquiry being made in the case.
The first requirement of Rule 702 declares that qualified experts can present opinions whenever the situation is a proper one for expert testimony (2). Similarly, Rule 104 reads that "Preliminary questions concerning the qualification of a person to be a witness, the existence of a privilege, or the admissibility of evidence shall be determined by the court, subject to the provisions of subdivision (II). This specifically pertains to conditional admissions." In making its determination, the court was not bound by the rules of evidence except those with respect to privileges. Rule 702 further demands that an expert's testimony be well-grounded in the standards generally followed in his or her field for validating assertions of the type offered.
The second requirement was intended to ensure the reliability or trustworthiness of the expert's testimony. Scientific evidence is deemed sufficiently reliable if the expert has "good grounds" for his or her testimony (i.e., the expert's opinion is based on "methods and procedures" of science rather than on "subjective belief" or unsupported speculation). The court further explained that this requirement should not be applied too severely to exclude all questionably reliable evidence. The ultimate touchstone of admissibility was helpfulness to the trier of fact.
The third requirement calls for the "fitness" of the facts to the evidence proffered. There must be a valid connection between the expertise in question and the inquiry being made in the case. When dealing with scientific evidence, this element is satisfied if there is a connection between the scientific research or test result presented and the factual issues being disputed in the case.
However, even if the scientific evidence satisfies Rule 702, it may be excluded by Rules 401, 402, and 403, and the probative value of the evidence asserted must also outweigh the prejudicial effect on the opposing party in order to be admitted. Rule 702 was further construed in Daubert v. Merrell Dow Pharmaceutical, Inc., which is now considered the standard of analysis to determine the admissibility of novel scientific evidence.
Daubert v. Merrell Dow Pharmaceutical
In interpreting Rule 702, the Court in Daubert explained that in order
for scientific evidence to be admitted into court it must satisfy a liberal
two-part analysis. The expert must testify to "scientific knowledge" that is
reliably based, and the testimony must "assist the trier of fact to
understand the evidence or determine a fact in issue." Rule 702 and
Daubert demand that the testimony be "well-grounded in the standards
generally followed in his or her field for validating the types of assertions
offered." It is the federal judge's sole responsibility to act as a
"gatekeeper" to ensure that the testimony is well-grounded and therefore
designated reliable scientific knowledge (3). The Court noted that
the subject of Rule 702 is the scientific validity of the proffered testimony
grounded in valid scientific methodologies and principles. Therefore,
pertinent evidence based on scientifically valid principles will satisfy the
requirements as stated in the Federal Rules of Evidence.
The first prong of the analysis and the essential focus of Daubert was whether the evidence was scientific knowledge that concerned the issue of the reliability of the technique offered for admission. As the Court noted, the adjective "scientific" implied something founded in valid methods and procedures of science or based on scientifically valid principles. Similarly, "knowledge" implied something more than mere speculation or subjective belief, but not necessarily ultimate certainty. As a result, the mere assertion by an expert that his or her testimony is scientifically valid would clearly fail the Daubert analysis. Under Daubert, for testimony to demonstrate "scientific knowledge," the evidence must be derived from scientific methods based on what is known (4). This important point distinguishes science from other forms of knowledge. Furthermore, the scientific knowledge requirement of evidence or testimony is established as a standard of evidentiary reliability or trustworthiness. Hence, in a case involving the admissibility of scientific evidence, evidentiary reliability would be based on scientific validity.
To determine whether the evidence or testimony is scientific knowledge and ultimately reliable, four factors must be considered: whether the technique or method has been tested (thus revealing its fallibility or validity), whether the known error rate of the technique is acceptable, whether the technique or method has been subjected to peer review, and whether the technique is generally accepted by the scientific community.
The Court of Appeals in Daubert v. Merrell Dow Pharmaceutical, Inc. on remand explained that these factors were "illustrative rather than exhaustive," and each was not necessarily relevant in every circumstance. The courts will use these factors liberally to determine whether the analysis on which the testimony is based falls within the range of accepted standards governing how scientists conduct their research and reach their conclusions.
Scientific validity Testing or fallibility.
Essential to the issue of reliability is the extent to which the method has
been tested. As the Court agreed, science cannot necessarily prove something
as immutably true; however, it can and does seek to prove something false,
thereby establishing its reliability. Thus, scientific knowledge is derived
by testing and retesting in an attempt to prove a hypothesis false. The more
diverse and severe the testing, the more reliable it is considered. As
Scheck stated, "While there is no scientific dispute about the validity of
the general principles underlying DNA typing, a particular method might not
be appropriate for a particular use" (5).
Before a method can be accepted for forensic use, it has to be rigorously characterized in research and forensic settings to determine the circumstances under which it will and will not yield reliable results. Furthermore, the focus of the fallibility requirement is not the conclusions generated, but rather the methodology and principles used. It is therefore essential to discern the basis of the expert's reasoning. Fallibility means more than just testing; it is reaching conclusions based on scientifically valid reasoning.
In assessing fallibility, a variety of considerations must be taken into account. First and most significant is what the Court stated was the subject of the Rule 702: the methodology/conclusion distinction. In Daubert, the Supreme Court explained that the requirements of Rule 702 envisioned a flexible inquiry. Its overarching subject is the scientific validity, and thus the evidentiary relevance and reliability, of the principles that underlie the proposed submission. The focus must be solely on the principles and methodology rather than on the conclusions they generate. It is clear that the persuasiveness of an expert's conclusions plays no role in the assessment of evidence admissibility, because science is defined through its processes-not its product (6). If an expert uses scientifically valid principles and methodologies to draw conclusions, his or her testimony is, by definition, scientific knowledge within the meaning of Rule 702 and therefore admissible. When attempting to have scientific evidence admitted, it is wholly inappropriate for the expert to argue the admissibility based on his or her conclusions. Such an approach will cast doubt on arguments concerning methodology by implying that the expert's arguments are too weak.
This is not to imply that the conclusion derived by the theory or technique is completely irrelevant. It must flow logically from the valid methodology. For example, suppose the results of a paraffin test were offered to show that the defendant had fired a gun because the test revealed traces of nitrates. Clearly, this conclusion would not pass the methodology or fallibility requirement because many different things can cause traces of nitrates to appear on a person's hand. However, if the evidence was offered to show only that traces of nitrates were on his hands, the conclusion would be derived from a valid methodology (the paraffin test) and would be accepted as scientific knowledge.
Another significant factor is the explanation of the process itself. A technique or theory is more likely to be admitted if the expert explains precisely how conclusions were reached and points out an objective source, such as a reputable scientific journal. This approach shows adherence to a scientific method that is practiced by at least a minority of the scientific community. Furthermore, detailed testimony explaining the scientific controls and the fact that the controls were accurately used can serve to demonstrate the reliability of the method as well as the results derived from it.
As the court explained in United States v. Martinez, "Daubert mandates that there be a preliminary showing that the expert properly performed a reliable methodology in arriving at his opinion." In that specific case, the Court of Appeals affirmed a lower court's decision that allowed into evidence testimony of an FBI forensic DNA specialist after it was shown that the expert was well qualified in this particular area. A detailed explanation of the procedures of DNA typing was presented, and the expert testified that he had followed the protocol and appropriately applied the quality controls during his research. The Court stated that experts trying to have scientific testimony admitted must submit affidavits attesting that he or she properly performed the protocols involved in the DNA typing. In Martinez, the court was careful to add that the inquiry into the admissibility of the evidence is flexible, and not all errors will cause the scientific evidence to be excluded.
It is clear that, in the case of a novel scientific method, literature might not yet be published on the topic or on the disagreements about the best method or controls. Alone, this is not enough to have the evidence excluded. In State v. Bullard, a North Carolina Court dismissed an argument by a defendant who claimed that a new technique for footprint analysis had previously not been allowed and accepted the new technique as reliable evidence on the basis of the expert's explanatory testimony, professional background, independent research, and the use of established methods.
An additional factor to consider is whether the evidence that the experts are proposing to testify to derives from research they have conducted independently of litigation or research done expressly for the purposes of testifying. As the remand decision of the Court in Daubert, Merrell Dow Pharmaceutical explained, "In determining whether proposed expert testimony amounts to good science, we may not ignore the fact that a scientist's normal workplace is the lab or the field, not the courtroom or the lawyer's office."
The Court went on to say that there are exceptions. For instance, once acquired, DNA fingerprinting and other forensic techniques closely associated with law enforcement may require the courtroom as the main theater of operations. Nevertheless, testimony flowing from research independent of litigation is less likely to have been biased toward a particular conclusion, because the expert is not limited to findings whose results will benefit his or her party's interests. Furthermore, independent scientific research carries its own indicia of reliability: Certain standards must be met for the expert to attract funding for a project. Consequently, testimony directly based on legitimate, preexisting research unrelated to the litigation provides a persuasive basis to conclude that the testimony was derived by the scientific method.
Finally, the severity or type of testing is an important consideration. What proof is there that the laboratory's method, when used by the laboratory itself and others independently, has been tested and will produce accurate results under conditions that replicate those encountered in actual casework situations? Daubert's insistence on testing demands proof that the technique has repeatedly produced accurate results under circumstances that replicate the proposed application. It has been proposed that the best way to show this would be through external proficiency testing by way of blind trials (6). This type of testing confirms an expert's method, not only in theory but also in practice, and no laboratory should let its results with a new DNA typing method be used in court unless it has undergone such proficiency testing via blind trials.
In summary, the focus of Daubert and the two most important considerations to bear in mind when attempting to have novel scientific evidence admitted are the importance of fallibility and the methodology/conclusion distinction. Although these factors alone are not dispositive, they are looked on by the courts as being of great weight.
Error rate. Closely associated with fallibility is a consideration of the potential error rate of the theory or technique at issue. Whereas fallibility seeks to ensure that the principles and methods underlying the theory or technique are valid, the purpose of error rate assessment is to show the validity and proper application of the theory or technique. Consideration of error rate is an important component in the Daubert analysis (7).
The basic theory behind error rate is that the fewer errors the technique is subject to, the more reliable the testimony when based on the results of the technique. Subsequently, a reasonably reliable determination of error rate is necessary. A technique with an unknown error rate likely has not been tested and therefore should not be admitted. There are no hard-and-fast rules to determine whether the error rate is acceptable. Nevertheless, where the potential error rate is high, the scientific evidence is likely to be disallowed.
Determination of error rate is similar to that of testability. Most important in this analysis is showing that the technique was properly performed and that, to whatever extent possible, steps were taken to prevent error. The best way to demonstrate a valid error rate assessment is for forensic laboratories to participate in a regular program of external blind proficiency testing on samples that replicate casework. Such a showing lends reasonable assurance of reliability to the opinion on which the error rate is based.
Additionally, the nature of the errors-if it is one that is relevant to the analysis-must be considered. As the Court stated in United States v. Martinez, "Every error in the application of the particular method should not warrant exclusion. An alleged error in the application of a reliable methodology should provide the basis for exclusion only if the error negates the basis for the reliability of the principle itself." The expert seeking to have scientific evidence admitted should be prepared to argue that reasonable steps were taken to rule out errors and that such an error rate is reliably based. Alternatively, if the error rate is high, the expert could argue that the errors were not such that they throw the reliability of the method into question.
Peer review or publications. The third factor announced by the Supreme Court in Daubert was the relevance of peer review of the technique or theory. As the court noted, submission to the scrutiny of the scientific community is a component of good science in part because it increases the likelihood of deleting substantive flaws in methodology. Consequently, it is generally believed that whether a particular theory or technique has yet to be subjected to scrutiny through publication, although not dispositive, is a valid consideration in assessing whether a technique on which an opinion is premised is methodologically valid.
In general, publication of one's scientific findings in a
well-institutionalized publication challenges the method for assessing the
plausibility of those findings. Federal courts consistently have stated that
findings not subjected to peer review should be regarded with skepticism.
However, the existence of specialized literature regarding the scientific
technique in question should be viewed as favorable. The inclusion of this
specific factor in the Daubert inquiry has been criticized by
academics and scholars alike. The logical assumption by the Court in
announcing this factor was that publication can often distinguish between
credible and incredible science. However, as one critic
Although the Court announced peer review as a relevant factor, the enlightened expert would not pin his or her hopes on this consideration. A more viable theory to proffer would be to focus on the results of peer review after publication. Obviously, if rigorous scrutiny of the published theory or technique has shown the method to be scientifically sound, the Court would consider this highly relevant.
The general acceptance requirement. How does Frye differ from Daubert? Although the Frye standard of general acceptance was displaced by the Supreme Court's decision in Daubert, the Court stated that whether the technique or theory had been generally accepted within the scientific community might yet be significant. Widespread acceptance can be an important factor in determining that evidence is admissible, whereas lack of acceptance can properly be viewed with skepticism.
Basically, Frye works as a total exclusion to any theory or technique that has not gained general acceptance in the community. Daubert, on the other hand, views acceptance as one of many factors that could show reliability. The Daubert standard also differs from the Frye standard in that its focus is on whether the methodology is generally accepted as opposed to whether the conclusions are accepted as in Frye. Certainly there are times when general acceptance could alone form the basis of admissibility. A theory that has been circulated among scientists and has uniformly been recognized as valid might be admitted. In the case of novel scientific evidence, the court would look to more specific indicia of validity.
The fitness requirement. The final requirement of Daubert is one that has been referred to as "fit." Rule 702 states that the evidence or testimony "must assist the trier of fact to understand the evidence or determine a fact in issue." Therefore, even if the testimony meets the first prong of the Daubert analysis, that does not guarantee it will be admitted. When offering evidence one must still demonstrate that the methodology has a valid scientific connection to the pertinent inquiry as a precondition to admissibility because, as the Court noted, scientific validity for one purpose is not necessarily scientific validity for other, unrelated purposes. The issue here is one of relevance. The expert seeking to demonstrate a fit between testimony and the fact in issue should explain in detail how the testimony is tied to the facts of the case.
The reverse is also true. An expert's theory does not pass the fit requirement merely because it relates to the facts of the case. The expert's opinion must be derived from a theory or technique that is capable of predicting the particular outcome about which there is testimony. In Porter v. Whitehall Laboratories, Inc., the plaintiff filed a suit in tort for injuries he allegedly suffered as a result of ingesting Ibuprofen. The plaintiff sought to offer scientific evidence that would tend to show that his renal failure had been caused by ingestion of Ibuprofen; however, the Court excluded the evidence because his expert was unable to say that Ibuprofen was the only cause. Thus, fit had not been met.
An example of admissibility: CE
CE provides information for forensic scientists who analyze evidence and give
expert testimony in the criminal justice system (8, 9). A
technique that can be used for the high-resolution separation of
biochemicals, CE offers the advantages of rapid analysis time, minute sample
size requirements, high efficiency, and economical operating cost.
The forensic scientist must often provide analyses of heterogenous mixtures, identifying each individual constituent. A unique requirement of the legal system is that a precise analysis must be made from very small samples while still preserving adequate samples for future analysis. McCord and Northrop have demonstrated the versatility of CE for the analysis of forensic samples exhibiting a wide range of chemical compositions, including gunshot residues, explosive residues, and drug and DNA identification (10). The demonstrated superiority of CE in resolution, cost reduction, and high reproducibility that yields a small rate of error has made this technique a reliable and flexible tool of choice as additional methodologies and analytical applications are developed (11).
Drug analysis. Drug analysis for legal proceedings account for numerous requests in any forensic lab. CE analysis allows separation of the drugs without causing decomposition or analyte loss from complex extraction steps. For chiral pharmaceuticals, the high efficiency of CE allows specific identification. For example, CE can distinguish between d-propoxphene, a controlled substance, and l-propoxphene, a legal one. In this case, evidence based on analysis by GC/MS would afford less information than that derived from CE.
CE also allows the drug fingerprinting of illegally manufactured drugs. If a researcher is using GC/MS analysis, certain mixtures of chemicals containing methamphetamine will derivatize the illegal drug into a compound that is not controlled, resulting in analysis that is at best inconclusive and thus nonadmissible in court. The use of CE methods, on the other hand, results in an analysis that doesn't change the original composition of methamphetamine.
Another application of CE methodology is in the bulk analysis of heroin and cocaine to determine origin of manufacturing and distribution. Because CE can identify the drug and metabolite impurities, the U.S. Drug Enforcement Agency is now using CE for general drug screening to quantitate heroin samples.
Gunshot residue analysis. Gunshot residue analysis has traditionally been based on the analysis of lead, barium, and antimony traces using AAS or scanning electron microscopy. The propellant in gunshot ammunition usually consists of nitrocellulose along with nitroglycerine, dinitrotoluene, diphenylamine, ethyl or methyl-centralite, and phthalate ester plasticizer. Manufacturers of ammunition, in response to environmental concerns over the use of lead and other heavy metals, now produce lead-free primers and ammunition. CE produces an excellent demonstration of organic gunshot residue constituents when smokeless powder is used. Firing range studies have demonstrated that gunshot residue collected using masking tape adhesive lifts could be identified using CE techniques (9).
Organic gunshot residue is also found in pipe bomb fragments. Materials such as black powder (a mixture of potassium nitrate, sulfur, and charcoal), flash powder, and ammonium nitrate are commonly used in the production of such explosive devices. Before CE was developed, ion chromatography, which was subject to multiple interferences, was the analytical tool of choice. CE, in contrast, allows for minimum peak interference and a wide range of ionic analytes.
Organic explosive residue. Often after terrorist attacks, the forensic scientist is called upon to identify organic explosive residue. The same CE techniques developed for gunshot residue analysis are used to identify explosive components, including isomers of aminodinitrotoluene, dinitrotoluene, and nitrotoluene (9).
DNA analysis. Forensic DNA identification in the legal system is used in criminal cases for the association or exclusion of suspects from the crime scene. Commercially available products prepared specifically for use with CE now afford proper sample preparation for DNA analysis, and CE is particularly useful in situations common to forensics where samples have degraded with time or are available in limited quantities. CE has been used to identify DNA in bone, blood, semen, saliva, and hair, and the analysis time is significantly shorter when using CE as opposed to traditional slab-gel electrophoresis techniques (12).
Given the economical and efficiency advantages of CE for forensic science and the judicial process, expert testimony based on CE analysis can be anticipated. The legal criteria of Daubert, as long as they are met by the scientific community, will allow CE and other legitimate scientific processes into evidence as acceptable expert testimony.
We would like to extend special thanks to Norberto A. Guzman, editor of the Journal of Capillary Electrophoresis, for his support and encouragement in the preparation of this article and to Evelyn Burnett for her patience in revising an infinite number of drafts.
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