Defendant, Joseph M. Spann, was convicted of sexual assault, a second-degree crime under N.J.S.A. 2C:14-2c(3). The statute criminalizes sexual penetration when the defendant has supervisory or disciplinary power, by virtue of his “legal, professional or occupational status” and when the victim is “on probation or parole, or is detained in a hospital, prison or other institution____” Defendant was a corrections officer at the Salem County Jail, where the victim was incarcerated on a detainer from the Immigration and Naturalization Service. Under those circumstances, intercourse itself is the crime, and here the proof of intercourse was strong, the verdict clearly sustainable even without the evidence challenged in this appeal. We find, however, as did the Appellate Division, that evidence was improperly admitted, and we cannot say that it was harmless. The admissibility of the evidence and harmless error were the only two points asserted in the State’s petition for certification following the Appellate Division’s reversal of the conviction. State v. Spann, 236 N.J.Super. 13, 563 A. 2d 1145 (1989).
As noted above, the only real issue, given the nature of the crime, was whether defendant had intercourse with the prisoner. Consent, force, or threats are irrelevant under the offense that was charged. The challenged evidence was that defendant was the father of the victim’s child, conception clearly having occurred while she was imprisoned. If he-was the father, criminal intercourse had occurred. The evidence consisted of blood and tissue tests, including human leukocyte antigen (HLA) tissue tests used to prove not that defendant was or was not
excluded
as the father but that he
was
the father. The specific item of that proof objected to by counsel was the State expert’s opinion, based on those tests, that the “probability” of defendant’s paternity was 96.55%. Obviously, that probability
The expert, testifying that the probability of defendant’s paternity was 96.55%, knew absolutely nothing about the facts of the case other than those revealed by the blood and tissue tests of defendant, the victim, and the child, and that defendant was the accused.
I
Use of Blood-Tissue Specimens to Prove Paternity; Calculation of Probability of Paternity; Use of Calculation in this Case
Until relatively recently, blood-grouping tests to establish paternity were admissible only to exculpate the accused in paternity cases.
N.J.S.A.
2A:83-3 (repealed by New Jersey Parentage Act,
L.
1983, c. 17, § 23). Science had proven, and there is apparently no question about the validity of the proposition and certainly none raised in this case, that certain blood specimens completely exclude others. Thus, blood specimen “X,” found at the scene of the crime and presumably that of the criminal, cannot come from an accused who has blood specimen “Y.” Similarly, blood specimens from mother and child that conclusively determine that only a man with blood specimen “X” could be the father eliminate a man with blood specimen “Y.” In such cases, if the accused’s blood was excluded, he was innocent; in paternity disputes, he was not the father. In New Jersey paternity cases, this limited use of blood tests, to prove only that defendant was
not
the father,
The lack of probative force of this evidence for the purpose of proving paternity was thought to warrant its exclusion. Its identifying factor, the fact for instance that 50% of the population, including the accused, have blood that could have produced a specimen matching that of the father, was deemed too insignificant to justify admission if offered as independent proof of paternity,
i.e.,
sufficient proof by itself. Even though insignificantly probative, it nevertheless was admissible as “a link in the chain of evidence” in criminal trials, just as the alleged assailant’s blond hair is used against a blond defendant.
See State v. Beard,
16
N.J
50, 58-59,
With the advent of multiple tests of blood samples, geneticists were sometimes able to exclude up to 72% of the population from certain blood types,
i.e.
given that kind of sample, those tests conclusively demonstrated that the sample could have come from only a limited portion of the population — 28% of it.
Joint AMA-ABA Guidelines: Present Status of Serologic Testing in Problems of Disputed Parentage,
10
Fam. L.Q.
247, 256-57 (1976) [“Joint AMA-ABA Guidelines”]. And with the discovery and development of HLA tissue testing — a test not of blood alone but of tissues of all kinds — the combination of blood and tissue testing, and on many occasions HLA testing alone, very often brought the exclusionary percentage to 95% and higher.
Ibid.;
D.H. Kaye, Plemel
As a Primer on Proving Paternity,
24
Willamette L.Rev.
867, 868 (1988)
When the portion of the population excluded ran as high as,
e.g.,
98%, it became intuitively obvious that if only 2% of the population could produce that sample and defendant was part of the 2%, it was not only consistent with his guilt, but tended to prove it — here that he was the father. Tests of blood and tissue samples started to be admitted not only to prove exclusion but also to prove paternity.
See Essex County Welfare
Precisely that kind of positive proof of paternity was used in this criminal case, as it had been in prior civil paternity cases without objection.
See, e.g., Jones v. Jones,
242
N.J.Super.
195, 200,
In calculating a final probability of paternity percentage, the expert relied in part on this 99% probability of exclusion. She also relied on an assumption of a 50% prior probability that
This figure was conveyed to the jury to mean what it says— this man is the father, or at least it is 96.55% probable that he is. It is not intended to and does not mean that he is part of a small group who might be the father (1% — and if there are 100.000 men in the relevant population, that “small group” adds up to 1,000 men). It means that even though there may be 1.000 others who fit the bill, he is the father — the odds are not 999 to 1 against the possibility of his being the father, but a 96.55% probability that he is. 3 If credited, the opinion is enormously persuasive.
1 X 1= 28 /.0357
(prior (likelihood (new odds) ratio) odds).
The reports of blood and tissue testing labs fairly regularly use this mathematical formula, calculating the probability of paternity figure based on the fifty-fifty assumption (that assumption sometimes referred to as the “prior probability,” to convey the sense that it is the probability of defendant being the father based'on all of the evidence in the case prior to any consideration of the blood and tissue test evidence). See Richard H. Walker, Guidelines for Reporting Estimates of Establishment, in United States Dep’t of Health and Hum. Servs., Essentials for Attorneys in Child Support Enforcement, app. C, 391, 392 (1986). Many of the experts who testify concerning the lab results also use the fifty-fifty assumption, following Joint Guidelines formulated in 1976 by the American Medical Association (A.M.A.) and the Section on Family Law of the American Bar Association (A.B.A.). Joint AMA-ABA Guidelines, supra, 10 Fam.L.Q. at 262.
On cross-examination defense counsel brought out the fact that the probability of paternity percentage was based on that fifty-fifty assumption. The expert described it as a “neutral” assumption. Since it supposedly favored neither the accused nor the victim, the expert said it gave the contention of each side (mother and purported father) equal weight and eliminated any subjectivity from the opinion. Her characterization of the evidence was that its “purely objective” nature was “one of the beauties of the test”; that it “makes no assumption other than everything is equal”; and that “the jury simply has objective information.” According to her testimony, there was no taking of sides, no judgment on the facts of the case. Defense counsel saw it differently. Counsel noted that even if it were conclusively proven that defendant had been out of the country at the time when conception could have occurred, this expert still would have concluded that the probability defendant was the father was 96.55%. Counsel’s observation was correct; the
The Appellate Division ruled that the probability of paternity percentage was inadmissible to prove intercourse because, in that court’s view, the calculation itself
assumed
that intercourse had taken place. 236
N.J.Super.
at 26, 563
A.
2d 1145 (citing
State v. Hartman,
The conclusion, however, is incorrect. The .5 prior-probability assumption (odds of 1) says only that the chance that defendant is the father is fifty-fifty, that it is just as likely that he is
not
the father as that he is, or that it is just as likely that he is as that any man chosen at random is. Those odds, for instance, are wholly consistent with a fact pattern that one and only one man had access to and intercourse with the victim and that one of two, and only two, men, including defendant, could possibly have been that one man, neither one more likely than the other to be the father. The fifty-fifty odds calculated into the probability of paternity percentage do not at all assume that defendant had intercourse with the victim; indeed, defen
But even on that correct understanding of the effect of the fifty-fifty assumption, a defendant could justly argue that it is totally unfair, indeed inadmissible, to ascribe even that substantial probability — 50%—to him, without the slightest regard to the facts of the case.
II
Enabling Jury to Use Its Own Estimate of Guilt Along with Expert’s Calculations of Probability of Paternity
For different reasons, however, we agree that the admission of the probability of paternity opinion as presented in this case was error. Although the jury learned, in cross-examination of the expert, of the expert’s assumption of a 50% prior probability that defendant was the father, the clear impression given by the expert was that it was somehow a “scientific” assumption, an accepted part of a scientific calculation, “objective,” “neutral,” “fair.” It is no such thing — although it is often, indeed apparently almost regularly, used by forensic experts testifying in paternity matters.
See
Mikel Aichin,
Some Fallacies in the Computation of Paternity Probabilities,
36
Am.J.Hum.Genetics
904, 906, 915 (1984) [“Aichin,
Fallacies
”] (asserting that although most paternity testers accept
More than that, we conclude that even if not objected to sufficiently by counsel, the expert’s opinion on probability of paternity did not satisfy the most fundamental requirement of expert testimony: its ability to aid the jury in its deliberations.
See State v. Kelly,
97
N.J.
178, 209,
The jury did not know, for instance, that even if it believed that the prior probability was half of the assumed prior probability, namely, .25 instead of .5, the formula would not at all result in cutting in half the ultimate result, the probability of paternity percentage. Indeed, it would still have left the proba
There is no contention in this case by defendant that the probability of paternity thus computed is inadmissible as such (at oral argument defense counsel said that the probability of paternity opinion was admissible if the jury itself found that the prior probability was .5). We therefore could conclude this opinion with the implicit holding above, namely, that a probability of paternity opinion is admissible but only if the expert notes that the calculations leading to that opinion use as one of the critical factors an assumed prior probability of paternity of .5. While this .5 assumed prior probability clearly is neither neutral nor objective, rather than prohibiting an expert witness from describing it as such, we would leave it to counsel to challenge this characterization through cross-examination. However, a jury should be required to use its own estimate of the prior probability of paternity, one based on all of the evidence in the case other than the scientific evidence arising from the blood and tissue tests; a prior probability, in other words, based on facts of which the expert has absolutely no knowledge — the facts of the case as they would exist were there no scientific tests, no scientific reports, and no expert. Furthermore, the expert’s testimony should be required to include an explanation to the jury of what the probability of paternity would be for a varying range of such prior probabilities, running, for example, from .1 to .9.
On this last point, we note that a similar approach, initially suggested by Professors Ellman and Kaye,
Probabilities and
Other courts have challenged the use of the fifty-fifty assumption.
See, e.g., County of Sonoma v. Grant W., supra,
184
Cal.App.3d
at 868, 229
Cal.Rptr.
at 301-302;
Everett v. Everett, supra,
150
Cal.App.3d
at 1070, 201
Cal.Rptr.
at 361;
Commonwealth v. Beausoleil,
397
Mass.
206,
In this somewhat abstruse area, therefore, procedures should be designed to avoid an outcome based on an unchallenged and unexplained .5 assumption of prior probability — unexplained and unchallenged because of the possible lack of knowledge of counsel. And these procedures should also obviate a jury unenlightened concerning the impact, on the probability of paternity opinion, of varying prior probabilities. Other prob
Ill
Admissibility of Probability of Exclusion and Paternity Index Based on Defendant’s Blood-Tissue Type
Given the controversies that exist concerning this matter— the admissibility not only of the probability of paternity opinion, but of the exclusionary percentage itself, as well as suggested conditions required in other cases that must be satisfied before such evidence is admitted,
see, e.g., Commonwealth v. Beausoleil, supra,
We note that the Appellate Division, in ruling on the admissibility of the probability of paternity opinion, properly ruled only on the propriety of the expert’s assumption of a 50% prior probability. 236
N.J.Super.
at 27,
We explicitly note here that in addition to the probability of exclusion, the related paternity index — if that has been calculated — is admissible at trial. It is, in effect, an exclusionary percentage that is based on additional blood tissue information resulting in a different likelihood ratio — usually higher than it would be without that information. Kaye,
Probability of an Ultimate Issue, supra,
75
Iowa L.Rev.
at 89-91. As we understand it, the exclusionary percentage, calculated by reference to a table of frequencies among the relevant population, is the result of the battery of tests that are usually made on a
The question of the permissible use of this kind of evidence is similar to that posed in
Landrigan v. Celotex,
127
N.J.
404, 414,
In Landrigan, we concluded, that the epidemiological evidence — the statistical likelihood that asbestos might have been the cause based solely on the greater occurrence of colon cancer in those who are exposed to asbestos — could be used along with other non-statistical “direct” evidence to support a conclusion of causation. In this case, instead of simply giving the jury both sets of facts — the underlying facts of the case and the related statistical evidence — and leaving to the jury the determination of the significance when both sets are put together, as we did in Landrigan, here a mathematical computation is added to the mix, one that purports precisely to calculate the probability of the ultimate issue. 5 The point here is that there is nothing fundamentally new in the use of blood-tissue tests to support the conclusion of paternity. What is new is the question of the admissibility of this mathematical formula to guide the jury in its use of the test information.
IV
General Admissibility of Expert’s Mathematical Calculation of Probability of Paternity
Because the issue was neither tried nor raised before us, we do not decide whether the probability of paternity opinion,
Without meaning to foreclose examination of any issue that the trial court deems relevant in making the admissibility determination, we suggest that the precise issue is rather narrow. We believe, from our readings, that Bayes’ Theorem, when applied in conventional probability analysis, is practically universally accepted as valid — certainly sufficiently accepted to conform to any requirement of “general acceptance in the relevant scientific community.” See Probability and Inference in the Law of Evidence ix (Peter Tillers and Eric D. Green eds., 1988) (“[E]ven the most rigorous critics of Bayesianism do not argue that Bayes’ Theorem is invalid”); Peterson, Paternity Tests, supra, 22 Santa Clara L.Rev. at 682 (“there is no dispute over the mathematical correctness of Bayes’ Theorem”). What is not at all clear is its general acceptance for the purpose of converting what is essentially a non-mathematical conclusion of a prior probability of guilt into a higher probability through the use of the formula.
The controversy, rather than the “general acceptance,” concerning the use of the probability of paternity opinion and Bayes’ Theorem or formula — indeed the evidentiary use of Bayes’ Theorem at all — is best reflected in the scholarly articles on this issue. See generally D.H. Kaye,
Presumptions, Probability and Paternity,
30
Jurimetrics J
323 (1990); C.C. Li & A. Chakravarti,
An Expository Review of Two Methods of Calculating the Paternity Probability,
43
Am.J.Hum.Genet
The disagreement on the subject is such as to prevent us from reaching any conclusion about “general acceptance.” What is needed is what the trial court will have: examination and cross-examination on that issue. It boils down to this: you have a mathematical formula that invariably works in converting a mathematical statistical probability into a new probability by using in that formula new information about the matter,
One of the ends of the argument is the meaning of the ultimate figure — here that the probability of paternity is 96.-55%. The expert translates that into “very likely,” based on the verbal predicate set forth in the Joint AMA-ABA Guidelines. Joint AMA-ABA Guidelines, supra, 10 Fam.L.Q. at 262. To a layman, 96.55% probability seems to correspond to something much stronger, highly likely, almost certain. But how is the jury to relate that percentage to the governing standard: “beyond a reasonable doubt”?
The formula is helpful, if one considers it helpful, because it tells the jury in mathematical terms just how strongly the blood-tissue tests may be deemed to point in the direction of paternity — here, converting an assumed probability of 50% into one of 96.55%. If valid, the expert’s opinion performs a service in helping the jury in such a case, for jurors presumably will have great difficulty in figuring out the significance of the likelihood ratio. Put differently, although the jury will intuitively and logically understand that the exclusion of 99 out of every 100 males as possible fathers increases the likelihood that defendant is the father, the jury will have difficulty in assessing just how
much
that likelihood is increased. The need for help in making that assessment is underscored when the typical arguments about the exclusionary percentage are considered— arguments so often made that one writer calls them “the
For all of these reasons, the trial court should conduct an
Evidence Rule
8 hearing, determining the expert’s qualifications and the satisfaction of the conditions attached to the admission of expert testimony,
i.e.,
“general acceptability” (see
Rubanick v. Witco Chemical Corp.
125
N.J.
421, 454,
Ordinarily, the conclusion that allows expert testimony in the first place — here “general acceptability” — is for the court. Furthermore, once it is made, depending on the circumstances, it can become the law for all future cases. We not only do not submit the question of the reliability of the breathalyzer to the
Since we have visited the subject fairly recently
(Windmere, Inc. v. International Insurance Co.,
105
N.J.
373, 386, 522
A.
2d 405 (1987);
Landrigan, supra,
127
N.J.
at 414, 605
A.
2d 1079;
Rubanick, supra,
125
N.J.
at 433-34,
An exception to the “general acceptance” standard is found in toxic tort cases on the issue of causation. Landrigan, supra, 127 N.J. at 414, 605 A. 2d 1079; Rubanick, supra, 125 N.J. at 433-34, 593 A. 2d 733. Recognizing the difficulties of proof of causation of cancer, and the apparent injustice of denying all recovery where the proof, although falling short of prior standards, is persuasive, we have allowed expert testimony, even though not generally accepted, where the facts and data relied on are of the kind that comparable experts would rely on, if the methodology or techniques used in converting those facts into an opinion are based on methodology that is similarly recognized by such experts as sound.
The “general acceptance” that is thought to impart sufficient reliability to the expert’s opinion as to warrant its admission is shown through the testimony of experts, through authoritative scientific or legal writings, or through persuasive judicial opinions.
State v. Kelly, supra,
97
N.J.
at 210, 478
A.
2d 364. Our readings, as suggested above, leave us with substantial doubt whether any one of the three methods of demonstrating general acceptance is present here. We know that general acceptance does not mean absolute or universal acceptance,
State v. Tate,
102
N.J.
64, 83, 505
A.
2d 941 (1986);
State v. Johnson, supra,
42
N.J.
at 171,
Clearly, the probability of paternity as derived from indices based on HLA serologic tests and computed with Bayes’ Theorem has achieved considerable recognition in the scientific community. The
Joint AMA-ABA Guidelines
specifically allow
We note also the explicit statutory provision permitting the use of blood and HLA tissue tests to “establish the positive probability of parentage,”
N.J.S.A.
9:17-51e,
i.e.,
paternity, in civil paternity cases. That provision also allows “[e]xpert testimony pertaining to these tests,”
ibid.,
suggesting that the probability of paternity opinion used in this matter is statutorily permitted in civil cases, although the statute is not that explicit.
6
The further statutory language allowing “[t]he court, upon application and for good cause shown, [to] limit the admissibility of blood tests or genetic tests,”
ibid.,
effectively safeguards against any potential in civil cases for prejudice arising from test results, presumably including the probability of paternity opinion. Various civil cases, however, seem to assume its admissibility. See,
e.g., Essex County Welfare Division v. Harris, supra,
189
N.J.Super.
at 482-83,
More than that, the above-cited statutory provision is the result of changes in the federal law designed to increase recovery from fathers failing to support children receiving Aid
Assuming the validity of this statutory direction in civil cases, see
Winberry v. Salisbury,
5
N.J.
240, 244-45,
We believe the provision in the statute concerning civil paternity cases, therefore, is persuasive but not at all dispositive of the admissibility of this evidence in criminal cases. Our rules concerning the admissibility of expert testimony must still be satisfied, as well as any special considerations that may pertain to proof in criminal cases.
Romano v. Kimmelman, supra,
96
N.J.
at 80,
Assuming the trial court finds the expert’s calculation of the probability of paternity admissible, we note some questionable restrictions on that admissibility suggested in case law. Several courts have instructed juries that they must disregard a probability of paternity figure unless they first find that the defendant had sex with the mother in the relevant time frame and under circumstances conducive to pregnancy.
E.g., Everett v. Everett, supra,
150
Cal.App.3d
at 1064, 201
Cal.Rptr.
at 361-63;
Commonwealth v. Beausoleil, supra,
Some cases have suggested that where the probability of exclusion is under 90%, or the resulting probability of paternity under 95%, the opinion should be excluded.
E.g., Commonwealth v. Beausoleil, supra,
In this case, the expert testified that, based on her interpretation of the
Joint AMA-ABA Guidelines,
a probability of paternity below 90% would not be useful. In fact, the recommended verbal predicates suggest only estimates below 80% are “not useful,” while the utility of estimates in the 80% to 90% range is “undecided.”
Joint AMA-ABA Guidelines, supra,
10
Fam. L. Q.
at 262. Nevertheless, if an expert wants to claim that the scientific community has concluded that a probability of paternity that is less than 95% is unreliable or irrelevant, the trial court of course will evaluate that testimony in a
Rule
8 hearing. Although we doubt that there will be any such testimony, or that if presented, that it will be persuasive, we note that those proposed conditions show the extent to which the use of the Bayes’ formula is not credited in the courtroom environment.
But cf.
National Institute of Child Support Enforcement, U.S. Department of Health and Human Services,
Essen
As a practical matter, the complex issues raised by admitting evidence of HLA test results in paternity and criminal cases are likely to become less and less important, indeed totally irrelevant, once acceptable scientific standards permit a broader forensic use of DNA “fingerprinting.” It is generally accepted that DNA identifying techniques will exclude from consideration the DNA sequences of all but identical twins, making DNA testing the functional equivalent of a fingerprint. Brad R. Byers, Comment,
DNA Fingerprinting and the Criminal Defendant: Guilty or Innocent? Only His Molecular Biologist Knows for Sure,
58
Ohio N.U.L.Rev.
57, 58 (1989); Eric S. Lander,
DNA Fingerprinting on Trial, Nature
501 (June 1989) . The complexity of the DNA testing procedures, and the apparently largely unregulated practices of those genetic laboratories equipped to conduct DNA testing in criminal cases, raise questions at this time concerning the potential reliability of such evidence in establishing paternity in criminal cases. Leigh C. Lawson, Comment,
DNA Fingerprinting and Its Impact Upon Criminal Law,
41
Mercer L.Rev.
1453, 1456 (1990); Peter J. Neufeld & Neville Colman,
When Science Takes the Witness Stand, Scientific American
46, 53 (May 1990).
But see United States v. Jakobetz,
V
Use of Probabilistic Analysis in Criminal Trials
The fundamental objections to the use of Bayes’ Theorem to establish probability of paternity are both mathematical and
The jurisprudential objection is different. It says that even if reliable, this factfinding method should not be used by juries except in the most unusual situations, or where the law explicitly requires a calculation of probabilities. In criminal cases, those objections go beyond the possibility of confusing or overwhelming the jury with mathematical complexities. They go to the heart of the jury’s function — the finding of guilt beyond a reasonable doubt.
These jurisprudential (and other) concerns are set forth in Laurence H. Tribe,
Trial by Mathematics: Precision and Ritual in the Legal Process,
84
Harv.L.Rev.
1329 (1971). Writing concededly in reaction to a perceived risk at the time that mathematics was about to take over the jury’s factfinding role, Professor Tribe persuasively argued that probabilistic analysis should but rarely be allowed to aid factfinding in criminal trials — and Bayes’ Theorem was very much in mind. Although expressly rejecting a
per se
exclusion of such evidence, his
One argument notes the possibility that the jury will use the associative evidence — the probability of exclusion — twice. First, having heard defendant has the blood-tissue type that the guilty suspect must have and that only one in one hundred have it, the jury will include that fact in its initial assessment of guilt, i.e., in its determination of the prior probability. When Bayes’ Theorem is then applied to that prior probability to reach a conclusion of probability of paternity, the calculation will necessarily again factor in the probability of exclusion, because it is part of the Bayes’ Theorem probability of paternity calculation, impermissibly using the exclusionary percentage twice. Id. at 1366-68.
Second, because Bayes’ Theorem will be introduced in the State’s case and because its use depends on the jury’s prior-probability finding, the jury inevitably will be impelled to focus, during the State’s case, before all of the evidence is in, on the probability of defendant’s guilt. Professor Tribe notes the inconsistency of that result with the presumption of innocence, the jury, of course, required to regard defendant as innocent until found guilty beyond a reasonable doubt. Id. at 1368-71. Simply put, the argument is that the use of that calculation during the State’s case impermissibly violates the jury’s obligation to keep an open mind until all of the evidence is in and deliberations start.
Third, the jury is implicitly asked to find defendant guilty beyond a reasonable doubt even though the probability of paternity itself has a quantifiable element of uncertainty and doubt. Id. at 1375. Stated otherwise, even if the probability of paternity is 95%, does our system of criminal justice encourage a jury to find guilt beyond a reasonable doubt when there is a 5% chance that defendant is innocent?
Finally, the argument notes the counter-intuitive impact of Bayes’ Theorem and the probability of paternity that can result.
Although some of these issues, both mathematical and jurisprudential, may ultimately become issues of law for this Court, we prefer to commit their resolution initially to the trial court where they will be subjected to adversarial testing. We are inclined to believe that appropriate jury instructions can cure all of them, or at least diminish their risk to the point that the advantages of the expert’s calculation outweigh these risks, assuming the opinion is otherwise admissible.
Given the guidance of the trial court and the argument of competent counsel, we think juries will be able to cope with the complexities and pitfalls of this kind of probabilistic evidence. Although the dispute on this subject presumably continues, we are not dealing here with some abstruse application of mathematics: the probability of paternity opinion is regularly and routinely used in civil cases and apparently favored if not mandated by both our Legislature and the federal government. The probability of paternity opinion is also routinely used by laboratories that perform this blood-tissue testing. We recognize, however, that if Bayes’ Theorem as applied to blood-tissue testing is admitted in this case, it is presumably admissible in any criminal case involving such blood-tissue testing.
VI
Summary
If the State in a criminal case offers expert proof of the probability of paternity, the trial court should hold a
Rule
8
In ruling on admissibility, the trial court should carefully consider the kind of testimony that the jury will hear. For example, if admissibility appears to depend on the validity of applying Bayes’ Theorem to a non-numerical jury assessment of the probability of paternity, the argument and testimony concerning that question of validity may be beyond the understanding of the jury. If that is the case, the trial court will have to determine the consequences — including possibly excluding the opinion or imposing practical limitations on trial testimony concerning the validity issue. Assuming it is concerned with potential confusion and prejudice, the court may, in a Rule 4 hearing, ultimately have to weigh the advantages and disadvantages, the costs and benefits, of the admission of the probability of paternity opinion. This necessarily will require a determination of whether substantially the same benefit — without some of the costs — can be gained through other evidence, e.g., the exclusionary percentage.
If the trial court allows this testimony — the opinion of probability of paternity — other matters, including conditions on its admissibility, should be considered. The expert should be qualified not only as a geneticist but also as a mathematician (which the expert in this case was not); or, alternatively, a mathematician should testify as well as the geneticist concerning the formula. The expert should explain the formula and indicate what it means, but should never be allowed to state that “in my opinion the probability of paternity ...” is a
Some of the above guidelines may be applied to civil cases where paternity is disputed, but we do not intend by this opinion to complicate or make more difficult the accomplishment of the apparent intent of the Legislature, namely, to enable the State or the mother to readily establish paternity through the use of both the exclusionary percentage and the probability of paternity opinion. That issue is not now before us.
In conclusion, we agree with the Appellate Division’s reversal of the conviction: the probability of paternity opinion was
We affirm the judgment of the Appellate Division. We remand the matter for a new trial in accordance with this opinion.
For opposition — None.
Notes
HLA types correspond to molecules, known as antigens because they react to specific antibodies found in blood as well as on all cells. The production of these antigens is directed by closely-linked genes, known as haplotypes, which are almost always passed as a unit from parent to child and exhibit a substantial number of variations in human population. D.H. Kaye, The Probability of an Ultimate Issue: The Strange Case of Paternity Testing, 75 Iowa L.Rev. 75, 88 (1989) [“Kaye, Probability of an Ultimate Issue"].
To illustrate how the HLA system works in identifying paternity: The child in this case had phenotypes (observable traits corresponding to some set of underlying genotypes) A2 A28 B45 B53, and the mother had HLA types A28 A30 B53 B61. These symbols refer to distinct antigens expressed by genes at two locations (the A locus and the B locus) in the human genome. These two genes, located next to one another on the same chromosome, typically are inherited as a haplotype, one from each parent. Id. at 88. Thus, the child receives one pair of A and B genes from both the mother and from the father. Because the mother and child have types A28 B53, the child must have inherited the haplotype A2 B45 from the father. Any man who did not possess this obligatory haplotype (A2 B45) could be excluded as a possible father. The HLA test showed that defendant’s phenotype was A2 A28 B35 B45, making him a possible father because he possessed the obligatory haplotype. The expert in this case testified that after factoring in the results of the HLA and other blood tests, the probability of exclusion was derived by consulting a table of haplotype frequencies that showed that only 1% of the relevant male population have the inculpatory blood and tissue type, and that the father is found only in that group. Thus, 99% of the relevant male population is excluded and could not be the father.
The expert nowhere explained how she specifically arrived at the calculation that led to the "probability of paternity" figure. Our understanding of the mathematics suggests that the actual exclusionary figure used was not 1% but rather 3.57%. Had she in fact used a 1% exclusionary figure, the probability of paternity would have been 99.01%, not 96.55%.
The 96.55% probability corresponds to odds of 28 to 1 in favor of defendant being the father instead of the 999 to 1 odds that he is not the father. The 28 to 1 odds correspond to 28 out of 29 chances, a probability of 96.55%.
Since the incidence of different blood groups, as well as HLA types, varies with race and to a lesser extent geography, gene-frequency tables are derived from population studies of different racial groups. The relevant population
The expert indicated that her results were subject to a sampling error of 3%. Her explanation of the impact of that error, however, was less than complete — indeed, on this record, beyond understanding. She noted that the 1% exclusion rate was based on a sample of 1,900 men, only 19 of them having the type of blood and tissues of a potential father. Conceding the 3% margin of error, she noted that would change the 19 to either 16 or 22 men, depending on which way the error went. But how 3% translates into that difference is impossible to determine. If the correct number were 16, then the exclusionary rate, instead of .01, would be .0084, 16% less than .01, yielding an even greater exclusionary figure and a substantially greater probability of paternity. If the correct number is 22, rather than 19, the exclusionary percentage would be about .0116, rather than .01, a 16% increase, and a correspondingly lower probability of paternity. The margin of error based on sampling, therefore, was acknowledged but on this record not at all adequately explained.
Obviously there are other differences between this case and Landrigan concerning the use of expert testimony. In Landrigan, the experts apparently could not have concluded that asbestos was the cause of death without using the epidemiological statistical evidence. In this case, the blood and tissue tests and the accompanying expert opinion based on Bayes’ Theorem are not essential; there is more than sufficient evidence to warrant submission of the case to the jury. What is added, of course, is evidence in the form of an expert’s opinion that not only supports a guilty verdict but, if credited, almost compels it.
The statute apparently was enacted six months after New Jersey inadvertently missed the initial deadline for state compliance with new federal welfare requirements. Continued noncompliance would have resulted in the annual loss of an estimated $20 million in federal funds to New Jersey. Paternity Testing Bill Is Sent to Governor, Star-Ledger, May 22, 1990, at 46.
The individual state welfare agencies are themselves responsible for contracting with “laboratories which perform ... legally and medically acceptable genetic tests which tend to identify the father or exclude the alleged father.” 45 C.F.R. § 303.5(c) (1991). In New Jersey, the Division of Economic Assistance within the State Department of Human Services has established specifications, which the State’s approved testing laboratories are obliged to follow in conducting HLA and other genetic testing. Notification of Award of Annual Contract for Genetic Testing, State of New Jersey, Dep't of Hum. Serv., Div. of Economic Assistance, for Contract Period Nov. 1, 1990, to Oct. 31, 1993. At a minimum, these tests must satisfy the current standards of, inter alia, the Joint AMA-ABA Guidelines. Id. at ¶ 6.1.7(1). As discussed above, these Guidelines recommend the use of the fifty-fifty assumption in calculating the probability of paternity percentage. Joint AMA-ABA Guidelines, supra, 10 Fam.L.Q. at 262.
Professor Kaye sharply refutes the merits of these "rules of evidence." Kaye, Probability of an Ultimate Issue, supra, 75 Iowa L.Rev. at 83-87. The particular evidentiary rules imposed by these courts are unlikely to have much effect on the admissibility,of the probability of exclusion, however, because the testing procedures of most laboratories already, on average, exclude more than 90% of the population. Id. at 98.