An introduction to the importance of dna evidence in criminal convictions

Before Daubert, many state and federal courts had construed their rules of evidence as not including a rigid requirement of general acceptance. A court could direct experts to address particular issues in their reports or pretrial summaries of testimony.

For example, research generally shows that subjects tend to revise their probability estimates in light of new information less than Bayes's theorem would predict reviewed by Beyth-Marom and Fischhoffand some research with mock jurors given written descriptions of blood-group evidence and various types of accompanying expert testimony also suggests that jurors will undervalue match probabilities see Faigman and Baglioni Conservative estimates deliberately undervalue the weight of the evidence against a defendant.

Individually small but collectively important procedural modifications have improved the technical quality of the DNA-testing process. Uniqueness is the limit as the frequency of a profile becomes smaller and smaller. In Chapter 5we noted that summing the frequencies of both bins, as recommended in the NRC report, will always give an upper bound on the allele frequency.

For many years, courts in criminal cases and paternity suits have admitted calculations based on allele frequencies derived from convenience samples for genetic markers, such as blood groups, HLA types, and serum proteins and enzymes.

But some experts might testify in qualitative terms even absent a claim of uniqueness; they might prefer to characterize profiles as "rare," "extremely rare," and the like.

The resulting plethora of questions about laboratory procedures and analyses initiated a second wave of cases in which various courts—including the supreme courts of Georgia, 20 Massachusetts, 21 and Minnesota 22 —excluded at least some aspects of DNA evidence.

Are ceiling frequencies sufficiently valid or accepted in the scientific community to be admissible. As for the possible misinterpretation of LRs as the odds in favor of identity, that too is a question of jury ability and performance to which existing research supplies no clear answer.

Rather, the expert presents the jury with a table or graph showing how the posterior probability changes as a function of the prior probability. However, no rule of law clearly compels such a limitation on court-appointed experts.

Does a profile frequency of the reciprocal of twice the Earth's population suffice. PCR-based test-evidence, however, is being introduced in a substantial number of cases, 30 and courts in each jurisdiction must decide whether this new mode of DNA typing satisfies the applicable test for admitting scientific evidence, regardless of whether RFLP-based evidence has been admitted.

In assimilating scientific developments, the legal system necessarily lags behind the scientific world. The argument that jurors will make better use of a single figure for the probability that an innocent suspect would be reported to match never has been tested adequately.

In Chapter 5we explained why the allele-frequency estimates from existing databases are suitable for computing genotype frequencies. Some issues that arise with regard to DNA testing seem particularly suitable for assistance from a neutral expert.

Given that such a decision might be made, we show how to do the requisite calculations. To counter the assumed threat, it proposed a procedure for placing an upper bound on the profile frequency—the "interim ceiling principle" discussed in Chapter 5 of the present report.

The sound-methodology standard is derived from phrases in the Federal Rules of Evidence. We hope that our review of the research will contribute to this process. None of the LRs that have been devised for VNTRs can be dismissed as clearly unreasonable or based on principles not generally accepted in the statistical community.

In fact, some have proposed that profile probabilities should be estimated from direct counts of profiles in the database.

DNA Evidence in Criminal Cases

However, determining whether quantitative estimates should be presented to a jury is a different issue. When the dangers of unfair prejudice, time-consumption, and confusion of the issues substantially outweigh the probative value of particular evidence, the trial court should exclude the evidence.

Furthermore, most current VNTR methods require radioactive materials, and the procedures are slow; it can take six weeks or more for a complete analysis.

In the remainder of this chapter, we elaborate on some of the developments that have occurred since the NRC report and on the scope of our review and recommendations. There might already be cases in which it is defensible for an expert to assert that, assuming that there has been no sample mishandling or laboratory error, the profile's probable uniqueness means that the two DNA samples come from the same person.

The Disagreement About Substructure As explained in Chapter 4the dispute about the "product rule" centers on the degree of population structure and the effect that it could have, in most situations, on the frequency of an incriminating profile in a racial group or, in a few cases, on the frequency within a particular subpopulation.

Expertise Experts who present and interpret the results of DNA tests must be "qualified by knowledge, skill, experience, training or education" Fed. Springfield v State, P. Although LRs are rarely introduced in criminal cases, 97 we believe that they are appropriate for explaining the significance of data and that existing statistical knowledge is sufficient to permit their computation.

Nonetheless, DNA testing provides a great opportunity for the falsely accused, and for the courts, because it permits a prompt resolution of a case before it comes to court, saving a great deal of expense and reducing unnecessary anxiety.

Even more recently, with the diffusion of PCR-based methods into the forensic realm, a fourth wave of cases has arrived. The likelihood ratio is still one step removed from what a judge or jury truly seeks—an estimate of the probability that a suspect was the source of a crime sample, given the observed profile of the DNA extracted from samples.

Procedures such as these might, for instance, persuade statistical experts to furnish a best estimate in addition to a range of estimates so that the jury will have a better sense of the degree of disagreement between the two sides.

The Importance of DNA Evidence

As emphasized in the report, the United States is not a homogeneous melting pot. and devoted personal time to discussions with ILJ staff on the role of forensic evidence in investigations and prosecution.

Considerable assistance was also provided by Mr. Gregg. DNA Evidence in Criminal Cases. DNA testing is now common in criminal trials and in proving innocence after wrongful convictions. DNA technology is rapidly becoming the method of choice when it comes to linking individuals with crime scenes and criminal assaults.

DNA evidence is increasingly used in criminal trials, and has also become a. We would like to show you a description here but the site won’t allow us. DNA Testing in Criminal Justice: Background, Current Law, Grants, and Issues Introduction Deoxyribonucleic acid, or DNA, is the fundamental building block for an individual’s entire convicting the wrong person, and establishing the innocence of those wrongly convicted.

DNA evidence is used to solve crimes in two ways. It describes the most important procedural and evidentiary rules that affect the use of forensic DNA evidence, identifies the questions of scientific fact that have been disputed in court, and reviews legal developmentsUnless otherwise indicated, our observations apply to all the technologies for DNA analysis described in this report.

One of the greatest tragedies in the criminal justice system is the conviction of a person for a crime he or she did not commit. Erroneous convictions can have immeasurable consequences for exonerees, original crime victims, and families.

An introduction to the importance of dna evidence in criminal convictions
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1 Introduction | The Evaluation of Forensic DNA Evidence | The National Academies Press