Plemel v. Walter
303 Or. 262, 735 P.2d 1209 (1987)
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Rule of Law:
Expert testimony regarding the 'paternity index' and its statistical equivalents is admissible in a filiation proceeding only if the expert clarifies that the statistic represents a relative likelihood compared to a random man and not the absolute probability of paternity, avoids misleading terminology, and, upon request, provides a range of probabilities based on various assumptions about the strength of the non-scientific evidence.
Facts:
- Dena Plemel's child was born on June 9, 1983.
- Plemel initiated filiation proceedings against Brent Walter, alleging he was the father.
- Plemel testified that she and Walter had intercourse once, on September 11, 1982.
- Walter admitted to having intercourse with Plemel but testified it occurred a month earlier, on the night of August 13-14, 1982.
- A nurse practitioner testified that conception would have been impossible in mid-August and estimated conception occurred between September 9 and September 16.
- Blood tests of Plemel, Walter, and the child were conducted, which did not exclude Walter as the father.
Procedural Posture:
- Dena Plemel initiated a filiation proceeding against Brent Walter in an Oregon trial court.
- The State of Oregon intervened as a petitioner.
- Walter filed a motion in limine to exclude expert testimony regarding the paternity index, which the trial court denied.
- At trial, the court overruled Walter's objection to the same testimony.
- A jury found by a 9-3 vote that Walter was the father.
- Walter (appellant) appealed to the Court of Appeals of Oregon.
- The Court of Appeals (appellee Plemel) affirmed the trial court's judgment.
- The Supreme Court of Oregon granted review.
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Issue:
Is expert testimony regarding the 'paternity index' and its statistical equivalents, such as the 'chance of paternity,' admissible in a filiation proceeding when presented in a way that may be confused with the actual probability of paternity?
Opinions:
Majority - Lent, J.
No. Expert testimony presenting the 'paternity index' and its equivalents is not admissible in a form that is likely to mislead the jury into believing it represents the actual probability that the defendant is the father. While such evidence is probative, its potential to cause unfair prejudice and confusion is substantial. The 'paternity index' merely compares the alleged father's likelihood of producing the child's genetic markers to that of a randomly selected man; it is not the ultimate probability of paternity. To calculate the actual probability, one must incorporate the strength of all other evidence in the case (the 'prior probability'), a task reserved for the jury, not the expert. Presenting a single statistic like a '99.4% chance of paternity' improperly assumes a 50% prior probability, thereby invading the province of the jury. Therefore, to be admissible, this evidence must be accompanied by specific explanations and safeguards to ensure the jury understands its limited, relative nature.
Analysis:
This decision establishes a critical gatekeeping framework for the admission of complex statistical evidence in Oregon paternity cases. It moves beyond a simple admissibility test to impose specific conditions on how an expert must present data to avoid misleading the jury. The ruling underscores the distinction between a relative statistical likelihood (the paternity index) and the ultimate legal question (the probability of paternity), ensuring the jury remains the ultimate arbiter of fact by weighing both scientific and non-scientific evidence. This approach significantly impacts how scientific experts must frame their testimony, requiring clarity and context over single, powerful-sounding statistics that could overwhelm a jury's independent assessment of the evidence.
