Court Opinion

ID: 9717448
Source: CourtListenerOpinion
Date Created: 2023-08-26 07:03:36.908068+00
Date Added: 2024-06-11T18:23:52.933513
License: Public Domain

Abrams, J.
(concurring, with whom Lynch, J., joins). I concur that the judgment should be affirmed. However, I believe that the judge correctly permitted the Commonwealth to offer the DNA evidence.
I do not agree that the DNA evidence offered by the Commonwealth in this case was inadmissible because the Commonwealth’s experts’ testimony concerning the background probability that the DNA matches in question were false was not presented numerically.1 In Commonwealth v. Curnin, *357409 Mass. 218 (1991), the court held that expert testimony concerning a DNA match must be accompanied by some background information indicating the probability that the match in question might have occurred by chance. Specifically, we said that “we would not permit the admission of test results showing a DNA match . . . without telling the jury anything about the likelihood of that match occurring.” Id. at 222 n.7, quoted in Commonwealth v. Lanigan, 413 Mass. 154, 159 (1992). The court did not declare that the likelihood must be stated numerically and in no other terms. Further, not all courts have said that the likelihood must be stated numerically. In Prater v. State, 307 Ark. 180 (1991), the Supreme Court of Arkansas stated that “[ejvidence of a DNA match made by a scientist who followed the proper laboratory protocol is admissible without drawing any statistical inferences. The scientist could simply testify to having performed the necessary steps and having determined that the two (2) samples examined match. The next step of extrapolating calculations as to the probability of random matches is not an essential step to DNA identification testing .. . .” Id. at 197. I think it is unfair to the Commonwealth to retroactively require the experts to state their opinions numerically.2
*358In their testimony, the Commonwealth’s experts testified at length in nonnumerical terms about the background probability that the DNA matches in question were false. Specifically, Doctors Cotton, Housman, and Keith each noted that the probes used in this case detect stretches of DNA that are highly variable between individuals (i.e., highly polymorphic). They each then observed that it would be highly unlikely for two DNA samples to match along one, let alone four highly variable stretches of DNA, as they did here, unless they came from the same person. Even the defendant’s own expert acknowledged that, if two sets of DNA samples matched along four highly variable stretches of DNA, it would be highly likely that they came from the same person.3
The nonnumeric background probability estimates offered in this case by the Commonwealth’s experts were based on their extensive reading of the relevant scientific literature and on their considerable personal experience in analyzing probe results. These estimates were based on scientifically reliable sources. I conclude that the trial judge correctly admitted the expert opinions.

In Commonwealth v. Lanigan, 413 Mass. 154 (1992), and Commonwealth v. Curnin, 409 Mass. 218 (1991), the Commonwealth offered numerical assessments of the likelihood that the DNA matches in question in those cases were false. The court held that these numerical likelihood assessments were inadmissible because they relied on a general population database which the scientific community did not generally consider to be reliable. The scientific community appears to have come to agreement on a means to correct for the DNA frequency calculation errors that might be associated with the use of a general population database. The National Research Council (NRC) has concluded that a numerical statistical analysis concerning the probability that a given DNA match is false which is based on a general population database would be reliable as long as the “ceiling frequency” approach was employed in making the calculation.
The “ceiling frequency” approach accounts for the impact that population substructure might have on a DNA frequency estimate by incorporating into its calculation “the greatest observed frequency of particular alleles within a given number of randomly selected population groups.” Lanigan, supra at 163. The NRC states that, by using the “ceiling frequency” approach in the calculation of DNA frequencies, the judicial system can ensure that “any error in calculating profile frequencies that is *357caused by population substructure [shall] accrue to the benefit of the individual against whom the DNA testing is being used.” Lanigan, supra at 163, citing the Report of the National Research Council’s Committee on DNA Technology in Forensic Science, entitled DNA Technology in Forensic Science at 3-13 (1992). Specifically, the NRC declares that any “ceiling frequency” based DNA match calculation would be “fair to suspects, because the estimated probabilities are likely to be conservative in their incriminating power.” Id. at 3-13.
If the NRC’s conclusion regarding the ability of the “ceiling frequency” approach to correct for the errors that might result from the use of a general population database reflects that of the general scientific community, a numerical assessment concerning the likelihood that a given DNA match is false which relies on a general population database could be admissible if the “ceiling frequency” method of calculation is employed by the expert.

The Commonwealth is not solely responsible for the absence of numerical probability assessments in this case. At various times during both the Frye hearing and the trial, the defense objected, on what appears to be a variety of reasons, to questions posed by the prosecutor which invited com*358ment on the statistical probability that the DNA matches in question were false.

At the Frye hearing, the prosecutor asked the defense expert, “Doctor, you agree that the probes that were used here are highly polymorphic, do you not?” The defense expert answered, “Yes, I do.” The prosecutor then asked, “And if there [were] matches on all four probes, . . . there is a great likelihood [that the DNA samples] would be from the same source, right?” The defense expert responded, “If there [were] matches, yes.”