Id. at 430-31.  

II. DISCUSSION  

1. Standard of Review  

At the threshold, we must determine the standard of review. Defendants argue that this court should review the trial court's ruling for an abuse of discretion. (7) Plaintiff argues that the question whether scientific evidence is admissible is reviewed for errors of law. We agree with plaintiff. In State v. Brown, 297 Or 404, 687 P2d 751 (1984), this court considered whether polygraph evidence was admissible. The court concluded that, "[n]otwithstanding the usual deference to trial court discretion, we as an appellate court retain our role to determine the admissibility of scientific evidence under the Oregon Evidence Code." Id. at 442. In O'Key, this court considered the admissibility of the horizontal gaze nystagmus (HGN) test to show that a defendant was intoxicated. The court stated that "[t]he validity of proffered scientific evidence * * * is a question of law * * *." 321 Or at 309 n 35.  

The O'Key court explained:  

"Although this court typically is deferential to a trial court's findings of preliminary facts under OEC 104(1), good reasons exist to modify this approach in the context of scientific evidence. Unlike almost all other preliminary fact questions made under OEC 104(1), a large component of the decision surrounding scientific evidence transcends individual cases. In the usual application of OEC 104(1), a trial court must make a context-specific factual determination. For example, a trial court must find by a preponderance of the evidence that a conspiracy existed before admitting evidence under the exemption from the ban on hearsay for statements made by a co-conspirator, OEC 801(4)(b)(E), and the trial court must similarly find that a hearsay declarant is 'unavailable' under OEC 804(1) for purposes of the statement against penal interest exception to the hearsay rule, OEC 804(3)(c). Because those preliminary facts are specific to the case before the trial court and do not repeat themselves in the same form in other cases, substantial deference to the trial court as factfinder logically flows out of the trial court's close proximity to the matter. When the preliminary facts are not case-specific, little or no deference to the trial court's findings is appropriate. The validity of scientific knowledge does not change from court to court; assessment of that knowledge should not change from court to court. "Moreover, if evidentiary rulings as to the admissibility of scientific evidence are reviewed with deference to trial court discretion, inconsistent decisions concerning the admissibility of scientific evidence may go unchecked from one trial court to another. Such inconsistency may confound efforts to provide uniformity under the Oregon Evidence Code."  

Id. at 320 n 45 (citations omitted). See also State v. Rogers, 330 Or 282, 308-15, 4 P3d 1261 (2000) (reviewing ruling that expert witness was not qualified to testify about possible causes of the defendant's frontal lobe dysfunction for errors of law). Accordingly, we review the trial court's ruling on Grimm's testimony for errors of law. B. Admissibility of Scientific Evidence In Brown, this court abandoned special tests for the admissibility of scientific evidence in favor of resolving the problem by relying on traditional evidence law as codified in the Oregon Evidence Code. 297 Or at 408. The admissibility of scientific evidence implicates three provisions of the evidence code. OEC 401 defines relevant evidence as  "evidence having any tendency to make the existence of any fact that is of consequence to the determination of the action more probable or less probable than it would be without the evidence."  

(Emphasis added.) 

OEC 702, which sets the standard for admission of scientific evidence, provides: "If scientific, technical or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, a witness qualified as an expert by knowledge, skill, experience, training or education may testify thereto in the form of an opinion or otherwise."  

OEC 403 permits the trial court to exclude relevant evidence  "if its probative value is substantially outweighed by the danger of unfair prejudice, confusion of the issues, or misleading the jury, or by considerations of undue delay or needless presentation of cumulative evidence."  

According to Brown, expert testimony is admissible if it is relevant under OEC 401, would assist the trier of fact under OEC 702, and is not subject to exclusion under OEC 403. 297 Or at 409. Scientific evidence "draws its convincing force from some principle of science, mathematics and the like. Typically, but not necessarily, scientific evidence is presented by an expert witness who can explain data or test results and, if necessary, explain the scientific principles which are said to give the evidence its reliability or accuracy."  

Id. at 407-08. This court also held:  

"In applying OEC 401, 702 and 403, this court must identify and evaluate the probative value of the evidence, consider how it might impair rather than help the factfinder, and decide whether truthfinding is better served by exclusion or admission."  

Id. at 409.  

The Brown court instructed:  

"In determining whether scientific evidence is probative under OEC 401 and the relevancy and prejudice analysis implicated in OEC 702's helpfulness standard, we believe [that seven factors] * * * provide structure and guidance * * *."  

Id. at 417. Those factors are:  

"(1) The technique's general acceptance in the field;

"(2) The expert's qualifications and stature;

"(3) The use which has been made of the technique;

"(4) The potential rate of error;

"(5) The existence of specialized literature;

"(6) The novelty of the invention; and

"(7) The extent to which the technique relies on the subjective interpretation of the expert."  

Id. at 417. (8) Those seven factors are not an exclusive checklist. Rather,

"the existence or nonexistence of these factors may all enter into the court's final decision on admissibility of the novel scientific evidence, but need not necessarily do so. What is important is not lockstep affirmative findings as to each factor, but analysis of each factor by the court in reaching its decision on the probative value of the evidence under OEC 401 and OEC 702."  

Id. at 417-18 (footnotes omitted).  

As noted in O'Key, a court should evaluate evidence that purports to be scientific to ensure that it is scientifically valid:  

"Evidence perceived by lay jurors to be scientific in nature possesses an unusually high degree of persuasive power. The function of the court is to ensure that the persuasive appeal is legitimate. The value of proffered expert scientific testimony critically depends on the scientific validity of the general propositions utilized by the expert. Propositions that a court finds possess significantly increased potential to influence the trier of fact as scientific assertions, therefore, should be supported by the appropriate scientific validation. This approach 'ensure[s] that expert testimony does not enjoy the persuasive appeal of science without subjecting its propositions to the verification processes of science.'"  

321 Or at 291-92 (footnote and citations omitted).  

2. Application of Legal Principles to this Case  

Plaintiff argues that the Brown and O'Key standards for admission of scientific evidence should not apply to Grimm's testimony, because his testimony "does not involve the application of scientific tests or statistical calculation, such as polygraph machines or DNA testing, where concerns regarding unfair prejudice and usurpation of the jury's role require a showing of scientific reliability of an expert's underlying methodology or process." Plaintiff's concerns might be appropriate in determining to what extent to apply the Brown and O'Key factors. See O'Key, 321 Or at 305 (multifactor inquiry is flexible; ultimate concern is scientific validity); Brown, 297 Or at 417 (factors "provide structure and guidance," but are not a checklist). However, plaintiff's concerns do not place Grimm's testimony entirely beyond the reach of Brown and O'Key. A jury is likely to believe that a doctor's testimony about medicine is a scientific assertion and, therefore, the proponent of the testimony must show that it is scientifically valid.  

Evidence is scientific when it "draws its convincing force from some principle of science, mathematics and the like." Brown, 297 Or at 407. "Propositions that a court finds possess significantly increased potential to influence the trier of fact as scientific assertions, therefore, should be supported by the appropriate scientific validation." O'Key, 321 Or at 292. Expert testimony regarding scientific evidence must bear a valid connection to the pertinent inquiry. The reliability of such expert testimony turns on whether it is scientific knowledge, which is determined by evaluating its scientific validity.  

Clinical diagnoses bear the marks of science. A medical doctor gathers information from a patient to develop a working diagnosis (a hypothesis), then uses that working diagnosis to gather further information or to specify tests that will confirm or refute the working diagnosis. Reference Guide on Medical Testimony at 463-64.  

"The goal of the clinician is to arrive at a diagnosis that can be used to develop a rational plan for further investigation, observation, or treatment, and ultimately to predict the course of the patient's illness * * *. To do this, the clinician must verify or validate the diagnostic hypothesis."  

Id. at 464. See also O'Key, 321 Or at 292 ("The scientific method is a validation technique, consisting of the formulation of hypotheses, followed by observation or experimentation to test the hypotheses.").  

This court previously has indicated that scientific evidence is subject to the requirements of Brown and O'Key, even though the science involved is not "hard" science. The O'Key court held that the state's evidence in that case was scientific, because it involved the premise that alcohol affected the automatic tracking mechanisms of the eyes. 321 Or at 295; see also State v. Milbradt, 305 Or 621, 630-31, 756 P2d 620 (1988) (psychological syndrome evidence is a form of scientific evidence).  

The question in this case is whether Grimm was entitled to testify about his opinion that silicone caused plaintiff's neurological conditions. In this inquiry, we focus on Grimm's methodology, not on his conclusions. See O'Key, 321 Or at 305 (focus must be solely on principles and methodology, not on the conclusions that they generate). After reviewing the record in this case, we conclude that Grimm's methodology was scientifically valid. Thus, Grimm was entitled to offer his opinion.  

The process of determining whether a substance causes a disease overlaps numerous areas of study. Epidemiology (9) is informed by clinical medicine:  

"'While epidemiologic information is at times derived from a much wider spectrum of biologic and medical disciplines, these three -- clinical medicine, pathology and biostatistics -- have almost universal application in epidemiology. Indeed, epidemiology may be thought of as the joint application of the three in the search for further understanding of disease etiology.'"  

George W. Conk, Against the Odds: Proving Causation of Disease with Epidemiological Evidence, 3 Shepard's Expert and Sci Evidence Q 103, 120 (Summer 1995) (quoting Brian McMahon and Thomas F. Pugh, Epidemiology, Principles and Methods (1970)) (emphasis added). Case reports based on clinical observations have recognized value in epidemiological research:  

"Case reports lack controls and thus do not provide as much information as controlled epidemiological studies do. However, case reports are often all that is available on a particular subject because they usually do not require substantial, if any, funding to accomplish, and human exposure may be rare and difficult to study. Causal attribution based on case studies must be regarded with caution. However, such studies may be carefully considered in light of other information available, including toxicological data."  

Reference Guide on Medical Testimony at 475 (emphasis added; footnotes omitted).  

"There plainly is a hierarchy to these different indirect forms of toxic effect evidence. Epidemiology is at the top, and structural similarity, in vitro testing, and case reports are at the bottom. Yet any one of these forms of evidence may have some utility in attempting to ascertain whether a causal connection exists."  

Michael D. Green, Expert Witnesses and Sufficiency of Evidence in Toxic Substances Litigation: The Legacy of Agent Orange and Bendectin Litigation, 86 Nw U L Rev 643, 658 (1992). An opinion drawn from only case reports can be troublesome, because it involves post hoc, ergo propter hoc (after this, therefore because of this) reasoning:  

"Some children who live near power lines develop leukemia; but does exposure to electrical and magnetic fields cause this disease? The anecdotal evidence is not compelling because leukemia also occurs among children who have minimal exposure to such fields. It is necessary to compare disease rates among those who are exposed and those who are not. If exposure causes the disease, the rate should be higher among the exposed, lower among the unexposed."