Opinion ID: 1375796
Heading Depth: 3
Heading Rank: 2

Heading: The need for statistics

Text: The court of appeals stated: An autorad match is meaningless without the statistical evidence to validate the match. If the autorad reflects only sites on the DNA that are common to all human beings (monomorphic sites), the evidence obtained cannot be the basis for identifying the defendant. Thus, the expert must also show that the alleles detected by the particular probes used are polymorphic. Hummert, 183 Ariz. at 484, 905 P.2d at 497. The purpose of the statistical interpretation of the match, however, is not to determine whether the loci measured in the autorad were poly- or mono-morphic. Because 99.9 percent of all human DNA is monomorphic  common to all people  the RFLP test has been developed to look at and measure only those areas that are polymorphic  i.e., known to vary widely from person to person. Statistical comparisons to the database are required to determine how often a particular polymorphic combination occurs in the population. All the sites used in the RFLP technique are by definition polymorphic, making a second test unnecessary. Related to the court of appeals' misunderstanding of the necessity of the statistical analysis of the probability of a random match was its application of a statement made by the National Research Council (NRC) in its 1992 report, THE EVALUATION OF FORENSIC DNA EVIDENCE (1992 Report), claiming that [t]o say that two patterns match, without providing any scientifically valid estimate ... of the frequency with which such matches might occur by chance, is meaningless. Id. at 74. Courts, particularly the Washington Supreme Court in State v. Cauthron, 120 Wash.2d 879, 846 P.2d 502 (1993), have interpreted this to mean that numerical statistics are required to express the significance of the match of two DNA profiles. We believe this view to be seriously incorrect. First, it is unclear that the NRC intended to say that only numerical expressions are acceptable in court. [4] Furthermore, in a later report, unavailable at the time of the court of appeals' opinion, the NRC stated: Scientifically valid testimony about matching DNA can take many forms. The conceivable alternatives include statements of the posterior probability that the defendant is the source of the evidence DNA, qualitative characterizations of this probability, computations of the likelihood ratio for the hypothesis that the defendant is the source, qualitative statements of this measure of the strength of the evidence, the currently dominant estimates of profile frequencies or random-match probabilities, and unadorned reports of a match. Courts or legislatures must decide which of these alternatives best meet the needs of the criminal justice system. NATIONAL RESEARCH COUNCIL, THE EVALUATION OF FORENSIC DNA EVIDENCE ES-7 (emphasis omitted) (1996) (pre-publication copy) (1996 Pre-Publication Report). We interpret this to mean that there is no single or specific scientific method of expressing the significance of a match but, rather, different ways of explaining the significance in a forensic setting. Therefore, once an expert witness, using a method such as RFLP that has been accepted as admissible under Frye, has determined there is a match, then the expert may testify and express his or her opinions in several ways that effectively communicate his or her findings. Id. From the scientist's standpoint, it is for the courts to decide if the expert may testify on the significance of the match as determined by probability statistics, or draw conclusions, as was done in this case, strictly from personal knowledge and study, if this is the type of information the expert regularly and reasonably relies on. See Ariz.R.Evid. 702 and 703. We did not foreclose this issue in Bible. We held instead that when DNA samples match, the conclusion is that they may be from the same individual. We went on to conclude there was no general acceptance in the scientific community for Cellmark's random match probability calculations and they were therefore inadmissible. Bible, 175 Ariz. at 590, 858 P.2d at 1193. We reserved and expressly [did] not decide whether the inadmissibility of the random match probability calculations means that other DNA evidence, such as evidence of a match is inadmissible.... We take a cautious conservative approach. Not knowing what records in other cases will show, what issues those cases will raise, or what new technology will bring, we neither write in stone nor go farther than we must.... We make no final judgment on how far, if at all, the court may go in allowing a party to inform the jury about the declaration of a match and its meaning in any specific case. Id.