Commonwealth v. Beausoleil

O’Connor, J.

(concurring in part and dissenting in part). I concur in the result reached by the court because I agree that it would be unfair to apply retroactively to the defendant the evidentiary rule announced today.

The bulk of the court’s opinion addresses the future admissibility of probability of paternity estimates based on HLA test results to establish paternity, and it is to that subject that I direct my attention. I agree that the HLA procedure is a tissue test, not a blood test, with the consequence that the admissibility of HLA test results and probability of paternity estimates based thereon is not controlled by G. L. c. 273, § 12A (1984 ed.). *225 I agree too, that, probable cause having been found, there is no constitutional impediment to a court order requiring a defendant to submit to HLA testing. Furthermore, I accept the court’s conclusion that HLA testing has gained general acceptance in the appropriate scientific community as a reliable indicator of the probability of paternity if it be established by other evidence that the defendant had intercourse with the mother at a time and under conditions that reasonably might have lead to the conception in question. I conclude, however, differently from the court, that, because the probability of paternity yielded by a statistical analysis employing HLA test results is premised on an assumption that that intercourse occurred, the test results should not be admitted in evidence unless that assumed fact is first established by a finding made by the trier of fact. That, of course, would require bifurcation of the trial, a procedure which is neither alien to our practice nor unduly burdensome, and, in my view, is dictated in paternity proceedings by considerations of fairness.

The court notes, ante at 211, that “the probability of paternity [is derived] by use of Bayes’ Theorem, a mathematical formula which describes the way newly discovered statistical information alters a previously established probability.” The court explains, ante at 211 n.6, that “[apparently, the most widely accepted way of calculating the probability of paternity involves an assumption that without regard to the HLA or other blood test results there is a 50% chance that the defendant is the father. This is termed the prior odds of paternity and is a constant. Bayes’ Theorem is then used to determine how the HLA test results alter this prior probability” (emphasis added). The court further explains, ante at 220-221 n.19: “There has been criticism of the probability of paternity statistic because it is based on a preliminary assumption of a 50% likelihood of the accused’s paternity. In other words [emphasis added], the calculation starts with the premise that the accused and one random male both had intercourse with the mother ‘at a time, and under circumstances, in terms of timing, fertility, frequency of coition, and use of birth control, making them both equally likely to have fathered the child’ (emphasis in original). Peterson, *226 [A Few Things You Should Know About Paternity Tests (But Were Afraid to Ask), 22 Santa Clara L. Rev. 667 ,] 685 [1982].” A relevant portion of Peterson’s article supporting the court’s understanding and giving enlightenment about the test’s assumption is set forth in the margin. 1

*227 No test tends to prove a fact it assumes. The HLA test, therefore, has no relevancy to the question, typically the one critical question in a paternity case, whether the defendant had intercourse with the mother at a time and in circumstances that would explain the conception of the child. Apparently, the court agrees, for it states that “HLA test results are not evidence of intercourse,” see ante at 220 n.18. The court also states that “the judge should instruct the jury, if he is so requested, that they may not consider HLA test results as evidence of intercourse, and that they may not consider such evidence of paternity unless they have found, beyond a reasonable doubt, that sexual intercourse at or about the time of conception had taken place between the mother and the alleged father.” Id. 2

Although HLA test results are not legitimately helpful to a resolution of the question whether a defendant had intercourse with the mother in relevant circumstances, it would be naive *228 in the extreme to expect fact finders, particularly inexperienced jurors, to ignore evidence of probability of paternity estimates based on HLA test results, presented through an expert, in determining the usually contested issue whether such intercourse had taken place. In the typical case, the mother asserts, and the defendant denies, the defendant’s involvement. The Commonwealth has the burden of proving the defendant’s involvement beyond a reasonable doubt. See Commonwealth v. Lobo, 385 Mass. 436, 445 (1982); Commonwealth v. MacKenzie, 368 Mass. 613 , 619 n.5 (1975). It cannot be said reasonably and with confidence that an expert’s testimony that the probability of the defendant’s paternity is 95% will not be misused by the fact finder to resolve the credibility issue in the Commonwealth’s favor. Even if an assumption be gratuitously made that the expert’s testimony will be fairly and clearly given and skillfully tested on cross-examination, the danger that the fact finder will be moved to decide between the conflicting claims on the basis of the expert’s testimony that the defendant “fits the mold” is inescapable. The portion of Peterson’s article quoted in n. 1 of my opinion supports that proposition.

The court recognizes the risk of which I speak, but, in my view, does not adequately appreciate or deal with it. The court counters the risk by requiring the judge, if requested in a jury case, to instruct the jury not to consider HLA test results as evidence of intercourse, and not to consider that evidence “unless they have found . . . that sexual intercourse at or about the time of conception had taken place between the mother and the alleged father.” Ante at 220 n. 18. Because the interests at risk are so substantial, the incidence of risk is so high, and a way to avoid the-risk is so simple, I am not content to meet the risk by simply requiring jury instructions.

“The naive assumption that prejudicial effects can be overcome by instructions to the jury ... all practicing lawyers know to be unmitigated fiction.” Krulewitch v. United States, 336 U.S. 440, 453 (1949) (Jackson, J., concurring) (citation omitted). See Bruton v. United States, 391 U.S. 123, 135 (1968) (“[T]here are some contexts in which the risk that the jury will not, or cannot, follow instructions is so great, and *229 the consequences of failure so vital to the defendant that the practical and human limitations of the jury system cannot be ignored”); Commonwealth v. DiMarzo, 364 Mass. 669, 681-682 (1974) (Hennessey, J., concurring) (“It is reasonable for us to be confident that in most cases limiting instructions accomplish their intended purpose. Nevertheless, in cases . . . where the evidence subject to limitations has an extremely high potential for unfair prejudice, we have a duty to be skeptical as to the effectiveness of limiting instructions .... The reasoning of the Bruton case is highly relevant. . . since that case recognized the futility, even the absurdity, of expecting a jury in some circumstances to conform to limiting instructions”).

Because of the futility in expecting triers of fact, especially juries, to comply with an instruction to ignore the probability of paternity factor based on HLA testing in determining whether the defendant had intercourse with the mother at or about the time of conception, I would hold that HLA based probability of paternity estimates are inadmissible except in the second segment of a bifurcated trial following a finding on that critical issue by the judge or the jury. After an affirmative finding, and within the limitations expressed by the court, ante at 217-221, I would hold the evidence to be admissible to show the probability that the defendant is the father of the child. Obviously, then, if the court were to accept my reasoning, the utility of HLA-based probability paternity estimates would be quite limited. Such evidence not only would be inadmissible in the absence of the above finding, but it would be superfluous in any case in which the fact finder (perhaps the jury in response to a special question) finds beyond a reasonable doubt that the defendant was the only one to have had intercourse with the mother at a relevant time. The test results would have value only in those cases in which it is open to the defendant to contend that, even though his act could have resulted in the conception, another man or other men, perhaps unidentified, also had sexual relations with the mother at a relevant time. It is at that time, and only then, that a probability of paternity estimate meeting the requirements articulated by the court is highly probative without being unfairly prejudicial to the defendant.

“In a paternity trial, a fact-finder is naturally tempted to seize upon statistical figures, like the paternity index or the probability of paternity, as lifelines of objective truth in a sea of prevarication. ‘Soft’ evidence involving difficult questions of credibility and other circumstantial matters may be submerged or lost because it appears unnecessary to resolve the questions in light of the hard, scientific, mathematical proof. Under these circumstances it is absolutely essential that the significance of the mathematical proof be clearly understood by both counsel and the fact-finder.

“The paternity index, and the probability based upon it, can be easily misused. Returning to the example of the man with a paternity index of 19 (probability = 95%), it is clear that in a large population many men will have a phenotype compatible with fathering the child. If only one man in a thousand were to have the proper phenotype, there would be 1,000 men who could have fathered the child in an urban population containing only one million men. Bayes’ Theorem cannot tell us which of these 1,000 men is the father. The most that the blood group evidence can tell us is that, assuming paternity is limited to the men in this city and the defendant is one of them, his probability of paternity is only one in a thousand, or. 1 %.

“The reason for this apparent discrepancy between the relative probability of 95% and the actual probability of .1% is clear if we again consider Bayes’ Theorem. The Theorem only tells us how to modify the prior odds of paternity in light of the new blood test evidence. The Theorem can do nothing to tell us what those prior odds are. Without the prior odds as a multiplier, Bayes’ Theorem is virtually useless.

“The paternity index merely represents the relative likelihood that a man with the phenotype of the accused father would contribute the required genes compared with the likelihood that a random man of the same ethnic group would do so. In order to convert this figure into the actual probability of paternity, we must also know the probability that the accused father had intercourse at the right time, and the probability that a random man did likewise. If the accused had no intercourse, then, regardless of his index, his probability of paternity is zero. If the accused is the only man to have had intercourse then, regardless of his index, his probability of paternity is 100%. The paternity index equals the odds of paternity only if it is assumed that the prior odds of paternity are 1:1 (or the accused is already 50% likely to be the father). In other words, before the paternity index accurately represents the odds of paternity, one must assume that the defendant had intercourse with the mother and that a random man (whom we shall call Mr. X) also had intercourse with her. In addition, the calculation assumes that both had intercourse at a time, and under circumstances, in terms of timing, fertility, frequency of coition, and use of birth control, making them *227 both equally likely to have fathered the child. If these assumptions are true, then, and only then, does Bayes’ Theorem accurately reflect the odds that the accused is the father.

“Since there is no way to calculate the prior odds of paternity, they must be inferred from the ‘soft’ evidence — the testimony of witnesses, circumstantial evidence, admissions and all of the other evidence which the fact-finder may prefer to ignore in favor of the ‘scientific proof.’ Until the fact-finder, disregarding the paternity index, is persuaded that the above assumptions are true, use of Bayes’ Theorem will yield a false result.

“Time and again, courts, commentators, and possibly even experts have disregarded the importance of the soft evidence and jumped hastily to the conclusion that the paternity index represents the actual odds of paternity. As a practical matter it may well be that justice is usually done because the soft evidence would justify the conclusion that the above assumptions are satisfied. The danger is that the habit of incorrectly applying these statistics will mesmerize fact-finders to such an extent that the statistics will be improperly used in cases where the soft evidence is tmly weak.” (Emphasis added.) Peterson, supra at 684-686.

HLA tests may be compared with fingerprint comparisons and the like as scientifically acceptable procedures to establish probabilities, as the court observes, ante at 217 n.15. However, it is important to understand that fingerprint comparisons are designed to show that the defendant was at the scene of the crime at a relevant moment, or that the defendant was in possession of a particular object related to the crime, while HLA tests are not designed to show that the defendant was “on the scene” at the critical time, but only what the probability of his paternity is if he was on the scene.