Opinion ID: 1813789
Heading Depth: 1
Heading Rank: 20

Heading: admission of statistical probability evidence

Text: We point out initially that there is nothing controversial about the theory underlying DNA typing, for there is a general scientific acceptance of the theory underlying DNA identification. See People v. Castro, 144 Misc.2d 956, 545 N.Y.S.2d 985 (1989). Freeman argues that the trial court erred in admitting the DNA evidence offered by the State, because the statistical probability analysis used to establish relevancy was not generally accepted within the scientific community. To aid in understanding Freeman's argument, we set forth a brief explanation of the science of DNA profiling. Additional discussions of the science of DNA and its use in forensics can be found in State v. Carter, 246 Neb. 953, 524 N.W.2d 763 (1994); State v. Houser, 241 Neb. 525, 490 N.W.2d 168 (1992); People v. Pizarro, 10 Cal.App.4th 57, 12 Cal.Rptr.2d 436 (1992); and the report of the Committee on DNA Technology in Forensic Science, National Research Council, DNA Technology in Forensic Science (1992) (hereinafter the 1992 NRC report). Contained in the nucleus of every human cell are 46 chromosomes, 23 of which come from the person's biological father and 23 from the biological mother. Each chromosome is made up of genes, the basic unit of heredity. Genes are composed of material known as deoxyribonucleic acid (DNA), which provides a genetic blueprint for cell reproduction. The DNA blueprint is the same in each cell of a person's body and does not change as the person ages. The differences between individuals are a function of the sequences of the building blocks in a single strand of DNA. For example, everyone has similar sequences in his or her DNA, but each individual will have a different number of sequences in a particular strand of DNA, and as a result, DNA strands can have varying lengths. These repeating sequences of building blocks are known as variable number tandem repeats (VNTR). The differences in the content and length of the sequences are known as polymorphisms, which are the basis of DNA identification. The location on a DNA molecule where a particular VNTR sequence occurs is known as a locus. A locus is polymorphic if the content and length of VNTR sequences vary from individual to individual at that particular locus. DNA profiling is done by looking at specific loci on human DNA which are known to be highly polymorphic, that is, where the VNTR sequences are highly variable. One person, for example, may have a VNTR sequence which repeats itself 10 times at a given locus, while another person may have the same VNTR sequence, but it repeats 100 times. Although there are several million distinguishable polymorphisms among individuals, examination of a small number of known polymorphic loci is sufficient for the purpose of DNA profiling. In criminal cases, a DNA scientist examines four loci along four separate chromosomes to find a DNA pattern. This is called RFLP DNA analysis. This process is performed on a body fluid sample taken from the suspect and a body fluid sample taken from the crime scene to determine if the two samples match. A comparison of the DNA profiles of the body fluid sample taken from the crime scene and the body fluid sample taken from the suspect is made. Based on this comparison, three conclusions can be reached: (1) The DNA profiles are a match, (2) the DNA profiles do not match, or (3) the comparison is inconclusive. From a finding of no match, one can conclude that the person from whom the sample was taken did not supply the body fluid sample taken from the crime scene. If the DNA profiles are a match, the VNTR sequence and the number of repetitions of that sequence at a particular locus on the DNA strand are identical in both the suspect's DNA and the DNA obtained at the crime scene. It is not accurate to conclude that the match is absolute, because the FBI typically looks at only four to six polymorphic loci on the DNA chain. It is conceivable that two people could have the same VNTR sequence and number of repetitions at the same locus on the DNA strand but have different sequences at other loci on the strand which were not tested. For this reason, in order for any of the DNA samples to be declared matches, there must be matches at all the loci tested. However, to be absolutely certain that the two DNA samples came from the same person, the entire DNA chain would have to be examined. This is not done, and consequently, one can call a matching comparison a match only to a degree of probability. The FBI employs certain principles of population genetics to assess the likelihood that a random sample of DNA selected from an identified ethnic population would match the known sample. The statistical significance of a match is measured by the frequency with which a particular pattern of VNTR sequences occurs at a particular locus within specific population groups. Alternate forms of the same gene are called alleles. A VNTR locus is the site of an allele pattern. The FBI has compiled databases of allele pattern frequencies for at least three different racial or ethnic populations so that probabilities may be calculated: Caucasian, African-American, and Hispanic. The FBI's Caucasian database was derived from blood samples of approximately 750 Caucasians. The African-American database was based on blood samples from 500 African-Americans, and the Hispanic database was compiled from blood samples from 500 Hispanic persons. The methodology employed by the FBI, as well as a number of other organizations doing DNA-profile probability calculations, is known as fixed-bin analysis. The term fixed-bin denotes a procedure by which the DNA scientist sorts polymorphic DNA strands by length and places them into predetermined bins. The frequency of a particular pattern of alleles is then compared to the frequency with which the same pattern of alleles occurs within one of the FBI's three ethnically specific population databases of polymorphic strands of similar size. The fixed-bin analysis is considered a conservative method of assessing DNA profile probabilities, since the frequency of allele patterns occurring in a random sample is higher than it would be if the bins were not utilized. Once the DNA scientist determines the probability with which one allele pattern occurs in a certain ethnic population, the DNA scientist must calculate the probability of all of the loci matches occurring within that population. One multiplication technique for determining the aggregate probability for the existence of a multiple loci match is known as the product rule. According to the product rule, the alleles at each locus are assumed to vary independently, and therefore, the population frequencies of the patterns at the several loci tested are multiplied together. This number gives the probability that the DNA profile of a person picked at random from a specific population would match the DNA profile of the suspect. See, generally, People v. Stremmel, 258 Ill.App.3d 93, 197 Ill.Dec. 177, 630 N.E.2d 1301 (1994) (discussing fixed-bin probability calculation method). Lynch testified that the DNA collected from the blood sample taken from Freeman matched each of the body fluid stains taken from the eight sexual assault victims on the basis of analyzing four different DNA loci markers. For seven of the eight matches, Lynch testified that according to the statistical calculations described above, the probability of randomly selecting an unrelated individual from the African-American population having the same DNA profile as Freeman is 1 in 6 million. The probability of randomly selecting an unrelated individual from the Hispanic population with the same DNA profile as Freeman would be 1 in 2 million. The probability of randomly selecting an unrelated individual from the Caucasian population would be 1 in 15 million. For the eighth match, the probability was higher, 1 in only 300, because fewer loci matches were compared. Freeman's assignment of error is premised on the assertion that the statistical probability analysis used to establish the relevance of the DNA evidence is not generally accepted within the relevant scientific community and therefore fails the  Frye test for the admissibility of novel scientific evidence. See Frye v. United States, 293 F. 1013 (D.C.Cir.1923). In State v. Carter, 246 Neb. 953, 524 N.W.2d 763 (1994), the issue before the court was whether the Frye-Houser requirement of general scientific acceptance applied to the statistical probability calculation step for DNA analysis. See State v. Houser, 241 Neb. 525, 490 N.W.2d 168 (1992). We held in Carter that the calculation of statistical probability was an essential part of the process used in determining the significance of a DNA match and that, therefore, the underlying method of the calculation must also meet the Frye-Houser general acceptance test. The Frye test has been used in Nebraska and was formally recognized in State v. Reynolds, 235 Neb. 662, 457 N.W.2d 405 (1990). The Frye test is not totally controlling as to the admissibility of novel scientific testimony, but is only the first of several criteria that a trial court determines are satisfied before such testimony may be admitted. See State v. Houser, supra . In State v. Carter, supra , we held that prior to the admission of DNA evidence, the trial court should hold a Frye hearing outside the presence of the jury to consider a six-part test for admission, to wit: (1) whether the witnesses on the DNA issue are experts in the relevant scientific fields, (2) whether DNA profile testing used in the case under consideration is generally accepted by the relevant scientific community, (3) whether the method of testing used in the case under consideration is generally accepted as reliable if performed properly, (4) whether the tests conducted properly follow the method, (5) whether DNA analysis evidence is more probative than prejudicial under rule 403, and (6) whether statistical probability evidence interpreting DNA analysis results is more probative than prejudicial. Freeman argues that the FBI's method of statistical interpretation of RFLP DNA profiling and determining the probability of a match, the fixed-bin method, has not gained scientific acceptance within the relevant scientific community and, therefore, is not admissible because it fails parts (2) and (3) of the above-described test. Freeman relies on the 1992 NRC report, which allegedly called into question the method used by the FBI to calculate the statistical probabilities regarding DNA profiles, and two cases which held that the specific statistical method used in Freeman's trial is not generally accepted within the relevant scientific community People v. Watson, 257 Ill.App.3d 915, 196 Ill.Dec. 89, 629 N.E.2d 634 (1994), and People v. Barney, 8 Cal.App.4th 798, 10 Cal.Rptr.2d 731 (1992). Therefore, we briefly summarize the criticism of the method of calculating the statistical probability of a DNA match. A population geneticist determines the frequency with which a specific allele or VNTR pattern occurs within a given human racial group. In the case of alleles that occur in the anonymous or polymorphic section of an individual's total genetic information, or genome, the likelihood that the samples will match is much smaller, and this reduced likelihood of matches is what gives DNA identification technology its value for forensic purposes. People v. Castro, 144 Misc.2d 956, 545 N.Y.S.2d 985 (1989). For the alleles to be random in the gene pool two pre-conditions must exist. First, the occurrences of the allele must not be caused by linkage disequilibrium, and second, the relevant racial population as a whole must be in Hardy-Weinberg equilibrium. For these purposes, a population is in equilibrium when there is no correlation between the allele contributed by the mother and the allele contributed by the father at a particular locus. That is, the alleles are independent of each other. Thus, when two alleles under examination appear on a single chromosome of the parent, the chance that the child received both alleles randomly is lessened. The reason for this is that there is an increased chance that alleles on a single chromosome will be passed on together and then become part of the child's genome. This is more likely than if the alleles were located on different chromosomes. Hence, there is less chance that the alleles were transmitted randomly. When this phenomenon occurs the alleles are linked, and for this allele the population is in linkage disequilibrium. Where the alleles occur on different chromosomes, linkage is not expected to occur except due to external forces of nature. Where there is no linkage, the appearance of the allele in a child may be said to have occurred randomly. When this occurs, the population is not in linkage disequilibrium. For purposes of Hardy-Weinberg equilibrium it is assumed that allele frequencies will remain constant within a population from generation to generation as long as mating remains random.... .... However, if the population is not in Hardy-Weinberg equilibrium then the alleles are not independent. Thus, the degree of dependency between the alleles must be calculated. Calculations may also be obtained by finding the actual, not projected, frequency in the population. This may be accomplished using larger populations, reference populations to determine genotype frequencies, or by considering only one allele. Conservative or reduced calculations may also correct the Hardy-Weinberg deviation problems. With deviations from Hardy-Weinberg equilibrium the frequency of the allele in the population, and thus the uniqueness of the fingerprint, can be in question but this is not necessarily related to the validity of the match. Id. at 967-68, 545 N.Y.S.2d at 992-93. Accord People v. Pizarro, 10 Cal.App.4th 57, 12 Cal.Rptr.2d 436 (1992). In summary, two scientists, Drs. R.C. Lewontin and Daniel L. Hartl, question the accuracy of the product rule discussed earlier. A fundamental principle of the product rule is that each allele is statistically independent and that one may calculate the probability of finding another person who has the same DNA pattern as the suspect by multiplying the probability of a matching VNTR locus by the probability of the other matching VNTR locus occurring in a specific FBI database. The study by Lewontin and Hartl suggests that the mating patterns of ethnic, religious, or other culturally significant substructures may affect the way in which alleles combine on a DNA chain. This means that if a member of a certain race were to mate with a person from the same race, there is an increased chance that certain alleles would be found in pairs on the DNA chains in their offspring. Lewontin and Hartl questioned the accuracy of the product rule because it does not account for the effect that a substructure population's mating patterns has on the location of alleles on the DNA strand. See R.C. Lewontin & Daniel L. Hartl, Population Genetics in Forensic DNA Typing, 254 Science 1745 (1991) (the 1991 Lewontin and Hartl article). See, also, Eric S. Lander & Bruce Budowle, DNA Fingerprinting Dispute Laid to Rest, 371 Nature 735 (1994). In State v. Carter, 246 Neb. 953, 524 N.W.2d 763 (1994), we determined that the task of this court is not to decide the underlying validity of the methods employed in calculating population frequencies, but to determine whether the methodology has gained general acceptance. Relying upon the 1992 NRC report, we concluded that the product rule had not gained general acceptance. In the case at bar, the trial court held a Frye hearing, at which the State offered the testimony of two expert witnesses regarding the DNA evidenceLynch, a special agent in the DNA analysis unit of the FBI, and Dr. Ranajit Chakraborty, a professor of population genetics at the University of Texas-Houston Health Science Center. Chakraborty testified that the fixed-bin method of calculating probability statistics regarding a particular DNA profile is currently generally accepted in the scientific community. Chakraborty stated that he was aware of the 1991 article by Lewontin and Hartl which made theoretical challenges to the use of the fixed-bin method. However, Chakraborty explained that advances in the study of DNA profile databases and the study of statistical probability issues since 1991 have answered the objections of Lewontin and Hartl and that the relevant scientific community now holds that the use of the fixed-bin method is appropriate for calculating statistical probabilities. Chakraborty testified that the current size of the databases used in the FBI's fixed-bin analysis is sufficient to answer Lewontin and Hartl's concerns about substructure mating patterns. Chakraborty stated that prior to the hearing, he had attended an international conference on DNA fingerprinting which was attended by more than 500 DNA scientists. One of the panel discussions he attended included a presentation on the compilation of the various DNA typing databases. The existence of these various databases indicates that the DNA typing databases are far more than sufficient to do any profiling probability calculation using the fixed-bin method. Chakraborty testified that empirical laboratory work has proved that the impact of possible genetic substructures is negligible. The current state of research is that the effect of substructures can be ignored for purposes of DNA typing data. Chakraborty also noted that Hartl published an article in approximately 1993 in which Hartl appeared to drastically change his opinion about the product rule. Chakraborty testified that in that article, Hartl changed his earlier conclusion that DNA typing, which used the product rule and fixed-bin analysis, should not be used in court. Moreover, Chakraborty testified that he had just presented a paper in which he analyzed the frequency of a certain type of DNA marker in more than 150 different subcultures of the world. Based on his analysis, he determined that the effect of substructuring on distribution of various genetic markers is very minimal. As a result, there is no population for which the Hardy-Weinberg principle, which is the theoretical basis for the product rule, does not apply. The State also placed in evidence Lander and Budowle's article, see Lander & Budowle, supra. In this article, Lander and Budowle, two experts in the debate over use of the product rule, report that the controversy which led to the 1992 NRC report and questioning of the use of the product rule has been resolved. The article suggests that the consensus of the relevant scientific community is that use of the product rule, though it is not the most conservative approach to DNA profile probability assessment conceivable, is sufficiently conservative to be used for the practical purposes for which it is used in a criminal case. The article states that the controversy over probability evidence and its use in the courtroom occurred over a misunderstanding of the 1992 NRC report. The article explains that contrary to what some lawyers and courts have determined, the 1992 NRC report did not entirely discredit use of the product rule in the courtroom. Instead, the 1992 NRC report pointed out that the ceiling approach was a more conservative method of calculating probabilities. The authors stressed that [m]ost important, the report failed to state clearly enough that the ceiling principle was intended as an ultra-conservative calculation, which did not bar experts from providing their own `best estimates' based on the product rule. This failure was responsible for the major misunderstanding of the report. Eric S. Lander & Bruce Budowle, Fingerprinting Dispute Laid to Rest, 371 Nature 735, 737 (1994). Lander and Budowle state that as a practical matter, the ceiling method provides an ultraconservative method of probability assessment which eliminates any concerns regarding the possibility of substructure influence on probabilities. However, the distinction between the ceiling method and the product rule method is largely irrelevant in the courtroom. Id. Freeman did not offer any rebuttal witnesses, but, instead, offered two exhibits: a copy of the 1991 Lewontin and Hartl article regarding the use of the product rule in DNA probability analysis and a copy of the 1992 NRC report. After hearing this testimony and receiving a number of journal articles and other professional materials regarding population genetics, the trial court concluded that use of the fixed-bin statistical probability analysis is generally accepted in the relevant scientific community. The trial court explained the basis for its determination as follows: The ... testimony is uncontradicted. It was that Lewontin and Hartl's theory was theory only and it has been discredited by the scientific community in the United States and worldwide as being a theory that just didn't work out at the lab. Therefore, the references in the Asa Carter by our Supreme Court are references that are no longer accepted by the scientific community in this country or anywhere in the world. They relied heavily in Asa Carter on Lewontin and Hartl's theory about subcultures, and the opinion goes on and on and on about the impossibility of getting a data base which would take it into account. [Hartl and Lewontin's theory] has been tested and disproved by the entire scientific community, and the conclusions reachedOr the theories have been discredited by at least all the scientific community that there's certainly no evidence that there's anyany controversy raging at all now. The evidence is overwhelming that the controversy that they created by their theories has long ended. Courts considering the admissibility of statistical probability evidence such as that at issue in the present case overwhelmingly confirm the trial court's decision to admit the evidence. See, People v. Johnson, 262 Ill.App.3d 565, 199 Ill.Dec. 931, 634 N.E.2d 1285 (1994); People v. Stremmel, 258 Ill.App.3d 93, 197 Ill.Dec. 177, 630 N.E.2d 1301 (1994); People v. Wesley, 83 N.Y.2d 417, 633 N.E.2d 451, 611 N.Y.S.2d 97 (1994); People v. Mehlberg, 249 Ill.App.3d 499, 188 Ill.Dec. 598, 618 N.E.2d 1168 (1993); State v. Dykes, 252 Kan. 556, 847 P.2d 1214 (1993); State v. Futrell, 112 N.C.App. 651, 436 S.E.2d 884 (1993); U.S. v. Bonds, 12 F.3d 540 (6th Cir.1993); State v. Montalbo, 73 Haw. 130, 828 P.2d 1274 (1992); Woodcox v. State, 591 N.E.2d 1019 (Ind.1992); People v. Adams, 195 Mich.App. 267, 489 N.W.2d 192 (1992); State v. Pierce, 64 Ohio St.3d 490, 597 N.E.2d 107 (1992); Kelly v. State, 824 S.W.2d 568 (Tex.Crim.App.1992); Satcher v. Com., 244 Va. 220, 421 S.E.2d 821 (1992); U.S. v. Jakobetz, 955 F.2d 786 (2d Cir.1992); Prater v. State, 307 Ark. 180, 820 S.W.2d 429 (1991); People v. Axell, 235 Cal.App.3d 836, 1 Cal.Rptr.2d 411 (1991); People v. Miles, 217 Ill.App.3d 393, 160 Ill.Dec. 347, 577 N.E.2d 477 (1991); People v. Lipscomb, 215 Ill.App.3d 413, 158 Ill.Dec. 952, 574 N.E.2d 1345 (1991); State v. Brown, 470 N.W.2d 30 (Iowa 1991); U.S. v. Yee, 134 F.R.D. 161 (N.D.Ohio 1991). These cases discuss a wide variety of materials addressing the controversy discussed in the 1992 NRC report, and each of these courts concluded that the widespread consensus of scientists involved in population genetics is acceptance of the use of the product rule for the determination of the relative probability of finding a match between a DNA sample from a suspect and DNA material found in a sample of body fluid recovered from a crime scene. It is also helpful to note that a recent case discussing use of DNA statistical evidence such as that at issue in the present case states that a 1996 update to the 1992 NRC report has concluded that use of the product rule is generally accepted in the relevant scientific community. In Commonwealth v. Rosier, 425 Mass. 807, 685 N.E.2d 739 (1997), the Massachusetts Supreme Judicial Court determined that the court's concerns with DNA statistical probability calculations in connection with the use of the product rule have been alleviated by the change in opinions within the scientific community regarding the effect of substructures on probability assessment. The Rosier court noted that the 1996 update to the 1992 NRC report clearly indicates that the concerns raised in the 1992 NRC report are no longer valid and that the product rule is a proper method of statistical probability analysis that is suitable for use in the courtroom. See, also, Commonwealth v. Fowler, 425 Mass. 819, 685 N.E.2d 746 (1997) (product rule now meets test of scientific reliability); State v. Kinder, 942 S.W.2d 313 (Mo.1996) (NRC has withdrawn criticism of product rule in 1996 report). Freeman argues that two courts have rejected use of the product rule on the basis of the 1991 Lewontin and Hartl article and the 1992 NRC report. See, People v. Watson, 257 Ill.App.3d 915, 196 Ill.Dec. 89, 629 N.E.2d 634 (1994); People v. Barney, 8 Cal.App.4th 798, 10 Cal.Rptr.2d 731 (1992). However, Freeman's reliance on these two opinions is misplaced. As this court did in State v. Carter, 246 Neb. 953, 524 N.W.2d 763 (1994), the Barney and Watson courts based their analysis on the state of the scientific evidence immediately following the 1991 Lewontin and Hartl article and the 1992 NRC report. Naturally, scientific opinion on a particular scientific matter is not static, and therefore, a determination of whether a particular type of novel scientific evidence is or is not generally accepted within the scientific community must consider the current state of the science. In view of the current scientific consensus affirming use of the product rule to assess the probability of a suspect's DNA profile, we hold that the trial court did not abuse its discretion in admitting the evidence of FBI probability analysis in Freeman's case. To the extent that Carter is based on an outdated level of acceptance of this evidence by the relevant scientific community, it is overruled.