Information Technology Reference
In-Depth Information
Plemel v. Walter
21
used Bayes' Theorem to derive the probability
of paternity.
“If the paternity index or its equivalents are presented as the
probability of paternity, this amounts to an unstated assumption
of a prior probability of 50 percent.” “. . . the paternity index will
equal the probability of paternity only when the other evidence in
this case establishes prior odds of paternity of exactly one.”
22
“. . . the expert is unqualified to state that any single figure is the
accused's 'probability of paternity.' As noted above, such a state-
ment requires an estimation of the strength of other evidence pre-
sented in the case (i.e., an estimation of the 'prior the probability
of paternity'), an estimation that the expert is no better position
to make than the trier of fact.”
23
“Studies in Poland and New York City have suggested that this
assumption [a 50 percent prior probability] favors the putative
father because in an estimated 60 to 70 percent of paternity cases
the mother's accusation of paternity is correct. Of course, the
purpose of paternity litigation is to determine whether the
mother's accusation is correct and for that reason it would be
both unfair and improper to apply the assumption in any partic-
ular case.”
24
A remedy proposed by the Court is of interest to us:
“If the expert testifies to the defendant' paternity index or a sub-
stantially equivalent statistic, the expert must, if requested, calcu-
late the probability that the defendant is the father by using more
than a single assumption about the strength of the other evidence
in the case. . . . If the expert uses various assumptions and makes
these assumptions known, the fact finder's attention will be
directed to the other evidence in the case, and it will not be misled
into adopting the expert's assumption as to the correct weight to be
assigned the other evidence. The expert should present calculations
based on assumed prior probabilities of 0, 10, 20, ..., 90 and
100 percent.”
25
21
303 Or. 262 (1987).
22
Id. 272.
23
Id. 275.
24
Id. 276, fn 9.
25
Id. 279. See also Kaye [1988].
