The Daubert Worldview
"If it come to prohibiting, there is not aught
more likely to be prohibited
-- John Milton, Areopagitica (1644)
Chapter 1: Some Basics
Here we will begin instead with a short refresher course on some basic legal concepts that will help to place Daubert within the larger framework of practical legal epistemology. Epistemology, of course, is a philosophical term denoting the theory of knowledge, and the term is chosen advisedly. It will be claimed here that the law does embody a practical epistemology -- one that divides intellectual labor by allocating inferential authority in various areas to discrete groups of persons playing defined roles.
This practical epistemology finds expression in a series of conceptual distinctions.
Law and Fact (and Judicial Discretion)
Lawyers and judges distinguish questions of fact from questions of law. These categories are usually defined functionally, by reference to the institutional bodies competent to decide questions in each category. It is simplest to begin with the jury's sphere of competence.
It can be flatly stated (for the world of civil litigation, at least) that juries decide only questions of fact. It can also be laid down, as a general rule, that only juries decide such questions, but this second proposition is subject to a qualification. In some cases, there is no jury, and the jury's functions are performed by some surrogate (usually the judge). Because this variability in the identity of the fact-finder usually entails only minor differences in the fact-finder's role and function, we will, in what follows, use the term "jury" as a synonym for "finder of fact," with the qualification assumed.
When it is said that juries decide questions of fact, it is implicit that the jury's decision is final. Of course, a jury's verdict is never "final" in the sense of being immune from judicial review. Indeed, the Seventh Amendment expressly contemplates just such review, in providing that "no fact tried by a jury shall be otherwise re-examined in any Court of the United States, than according to the rules of the common law." Under those "rules of the common law," a trial judge, or an appellate court, may undo a jury's verdict if the court concludes that the jury was improperly asked to resolve questions in categories beyond its institutional competence -- e.g., questions of law. A court may also overturn a verdict if no reasonable jury could reach that verdict on the evidence of record. In both cases, however, judicial reversal is permissible only because the jury was asked to decide an issue that turns out not to have been a true question of fact in the first place. This may seem circular, and it is. By definition, any question properly resolved by the judge, as opposed to the jury, is not a question of fact, and so if a judge may overturn a jury's finding, it follows that the issue was nonfactual from the start (on that particular evidentiary record, at least).
There is another way to put the same point. Implicit in the concept of decision is the existence of a range of permissible decisions. If no jury decision is permissible on some issue, or if only one "decision" would be permissible, then plainly there is no real "decision" for the jury to make, and thus no true question of fact arises. Moreover, even in cases where some range of permissible decisions exists, the jury may make a decision falling outside that range. For example, it may be that from the evidence of record in a given case, a reasonable jury could award compensatory damages in any amount falling between zero dollars and one million dollars. A damage award falling outside that range will be overturned as "clearly erroneous" -- that is, it will be deemed erroneous "as a matter of law." Within the jury's permissible range of decision, however, the jury's award will be final, in the sense that no higher authority can later decide the question of fact differently.
Jury finality applies only to the parties to the litigation (along with persons associated with the parties in such a way as to render the jury's verdict binding on them as well). This means that "questions of fact" may be decided differently in different trials between different litigants. Suppose -- hypothetically -- that I say: "Whitney Houston assaulted Britney Spears." The jury deciding Whitney Houston's defamation claim against me may conclude, in evaluating my "truth" defense, that my statement was inaccurate. However, the different jury subsequently deciding the assault claims in the case of Britney v. Whitney may potentially decide, based on the identical evidence, that Ms. Houston did indeed attack Ms. Spears, which would make my hypothetical statement valid. This potential for "inconsistent" verdicts is one reason, perhaps, why it is not customary to speak of jury verdicts as being "true" or "false." Propositions that can be "true" or "false" normally obey logic's Law of Contradiction, which holds that a proposition cannot be both. "Facts" found in successive jury verdicts, evidently, do not obey this principle. The reason is straightforward. What is wanted from the jury, in the end, is not "truth," but rather a "finding" that will be deemed dispositive in the practical resolution of some particular dispute, and the adversary system places in the hands of the parties to that dispute the decision what evidence to proffer in the advocacy of one finding over another. Of course, the rules of evidence are supposed to help ensure that the jury decides such questions with an eye to what is true. But we'll come to that.
We may meanwhile observe that juries do not define the range of their own permissible inferences from a given set of evidence. That is a question of law. Like other questions of law, it is decided by trial or appellate judges.
From what has been said so far, it might be supposed that just as a question of fact is whatever a jury has institutional competence to decide, so too a question of law is whatever judges may legitimately decide. But this oversimplifies, because judges, and especially trial judges, also make decisions on issues that are not questions of law, within a domain often described as their sound judicial discretion. Decisions about the admissibility of evidence, for instance, are often said to fall within this discretionary realm.
How do questions of law differ from questions of judicial discretion? A functional definition can again be supplied. If a range of judicial decisions is permissible, then the question is one of judicial discretion. If only one decision is permissible, then the issue is one of law. Just as the scope of a jury's permissible decisions is a question of law, so too is the scope of a trial judge's sound judicial discretion. When judges render decisions outside the scope of their sound discretion, they are said to abuse it.
The foregoing can be summarized in a simple table.
The finality of jury dispositions on questions of fact suggests that juries' factual findings are important. They are also important because the law assigns many key issues to this category -- e.g., whether conduct is blameworthy, whether the blameworthy conduct caused legal injury, and the measure of compensation to be afforded as a result. Because such questions lie at the heart of many disputes, juries wield great power. Indeed, that power is sometimes viewed with disquiet, on the ground that jurors, being fallible human beings, may be swayed by considerations that should not affect their decisions. For example, a jury might award damages to an injured plaintiff not because the jury actually believed that the defendant engaged in conduct that caused the plaintiff's injury, but merely because the jury wanted to ease the plaintiff's suffering and believed that the corporate defendant would not miss the money. This would be an example of simply taking something from person A to give it to person B.
To help forestall such miscarriages of justice, the law regulates advocacy. One aspect of that regulation is the law of evidence.
Personal Knowledge, Hearsay, and Opinion
As just suggested, jurors are expected to reach their decisions based on admissible evidence. A Martian anthropologist might view this as odd. In most spheres of American life, after all, the law does not regulate inquiry or discourse very closely. Politicians, for example, are free to publish rank nonsense, if they believe it will promote their chances of election, and voters are free to believe rank nonsense if they want to. It is thought, on the advice of great thinkers, that the marketplace of ideas will sift truth from falsehood, and fact from hype -- well enough, at any rate, for purposes of governance. This also happens to be the legal standard governing the normal conduct of scientific inquiry, of which more anon.
In courtrooms, by contrast, discourse is very tightly regulated. It is not obvious that things had to be this way. One can imagine an adversary system structured on the model of debate, where each side is free to say whatever it pleases, backing up its assertions however it may. But that is not our system. Our system ties jurors' permissible inferences to evidence -- i.e., to material that is disclosed to the jury only if it clears certain technical hurdles thought pertinent to its worthiness of consideration.
Evidence comes primarily from the sworn testimony of witnesses. With certain well-defined exceptions, witnesses may testify only concerning subjects on which they possess, or claim to possess, personal knowledge. The concept of personal knowledge evades sharp definition, but speaking very roughly, personal knowledge comprises that which a person knows, or claims to know, via direct employment of the person's five senses. (There have been lively debates, in the philosophical community, about whether any proposition can ever express pure, uncharacterized sensory data. We are not concerned, for the moment, with such debates. For the moment, we are speaking in the everyday sense, in which we know that a red car was parked in the driveway because we saw a red car parked there.)
Personal knowledge is often distinguished from hearsay. The technical legal rules governing hearsay are convoluted. The basic concept, though, is simple enough. Testimony is hearsay if the fact or event in question was not directly observed by the witness, but is believed by the witness to be true based on what the witness has read or heard other people say.
It will be observed, immediately, that most human knowledge relies radically on hearsay. Indeed, in many ordinary contexts, hearsay knowledge is considered superior to direct observational report. In the courtroom, however, the general rule -- subject, once again, to certain well-defined exceptions -- is that hearsay is inadmissible.
In addition to facts within their personal knowledge, all witnesses are also competent to testify to their opinions, if these are rationally grounded on facts that are within the witness's personal knowledge. The line between opinions, on the one hand, and facts known by direct personal knowledge, on the other, is often fuzzy, and most lay testimony could be viewed as falling somewhere on a spectrum between these two points, or as including elements of each. By way of illustration, however, we can say that a witness who saw the butler may testify to the witness's personal knowledge of the butler's facial expressions. However, if the witness testifies, based on the butler's facial expressions, that the butler "was nervous," then the witness would usually be thought to be offering an opinion, since "nervousness" is considered to be a state of mind not directly accessible to sensory inspection. For lay witnesses, no real consequences flow from this distinction -- except the consequence that testimony is not rendered inadmissible simply because it arguably incorporates an element of opinion. (Any testimony, of course, may be excluded if gratuitously prejudicial. Name-calling, for example, is not allowed.)
Lay Testimony and Expert Testimony
The personal knowledge requirement just discussed applies, in general, to lay testimony. A defining feature of expert testimony is that the personal knowledge requirement is suspended. A qualified expert, that is, may testify to matters not within the expert's personal sensory experience, and to opinions not ultimately based on personal knowledge. This means not only that experts may testify based on hearsay reports of sensory observations made by others, but also, in principle, that experts may testify to propositions not ultimately based on anyone's sensory observations at all. This is what happens, for example, when an economist testifies that a profit-maximizing firm in a competitive market will expand production until its marginal cost per unit of output equals the market price for that unit. The economist is not reporting, here, on anyone's sensory observations. The economist is testifying about abstract economic theory, which he or she learned from listening to professors and reading books.
Now the truth, of course, is that even lay reports of personal knowledge can incorporate vast admixtures of tacit theory. Lay witnesses may testify, for example, to the price of milk at their local grocer, even though no one has ever seen a price. What the witness has actually seen, perhaps, is a price tag. Because the witness is familiar (largely via hearsay) with the prevalent social practices governing economic exchange, the witness is able, from the price tag datum, to predict what conditions the grocer would exact before the witness could leave the store with the milk, and to make this prediction at a high level of confidence. Shall we say that the witness's testimony about the "price" of the milk is really opinion testimony based on the witness's personal knowledge of the price tag? This seems artificial, and little would be gained by the artifice. It is simpler to admit straightforwardly that even the most basic reports of sensory observation contain an unavoidable component of interpretation (cf. "A red car was parked in the driveway"), and to say that lay witnesses are permitted to employ common sense and common practical knowledge in their characterizations of their sensory observations.
The theories that experts may bring to bear, by contrast, are not confined to those incorporated in the common fund of common sense. Indeed, they may testify as experts only if they can claim scientific, technical, or other specialized knowledge that will help the jury to understand the evidence or determine a fact in issue. Under Fed. R. Evid. 702, this specialized knowledge may be derived from experience, training, education, or (begging the question) "knowledge." The issue whether the expert possesses specialized knowledge thus derived -- i.e., whether the expert is qualified -- is decided, in the first instance, by the trial court in its sound discretion. In practical terms, only persons occupying recognized niches in the socially accepted taxonomy of knowledge will usually qualify. Judges are generally loathe to recognize the bare existence of specialized "knowledge" on its face, even though the literal terms of Rule 702 might permit this. Judges want to know how the expert's specialized knowledge came to be, and almost invariably, they also want to assign it to some generally recognized "field." Usually, therefore, the expert must have the imprimatur of late capitalism in the form of relevant occupational experience, or a university's imprimatur in the form of a degree, or the state's imprimatur in the form of a license or certification -- or all three.
Once qualified, Rule 702 says that experts may offer testimony concerning their expert knowledge "in the form of an opinion or otherwise." The distinction being drawn here is not quite the same as the distinction between lay testimony based on personal knowledge and lay opinion testimony. This distinction relates, roughly speaking, to whether the expert purports to be applying the expert's specialized knowledge to the specific circumstances of the case. If he or she does, it is usually said that an expert opinion is being offered. It is not required that an expert's testimony be offered in the form of an opinion. The rules permit an expert to testify to general scientific or technical principles, leaving their application to the jury. In practice, however, experts generally offer their conclusions (opinions) about fact patterns presented in the case. A short list of common examples would include:
From even this short list, it should be obvious that expert testimony is a potentially dangerous weapon. As we have seen, the law regulates jury verdicts in two ways: before the fact, by the exercise of judicial discretion in policing the evidence that juries may hear, and after the fact, by limiting as a matter of law the scope of the jury's permissible inferences from whatever evidence is admitted. The second method will frequently be much less efficacious with expert testimony, because the subject matter of expert opinion is often parlously close to the ultimate issue of fact to be decided by the jury, so that there is very little by way of jury "inference" to regulate. Together, the hearsay rule and the personal knowledge requirement tend to keep lay testimony (even lay opinion testimony) safely distant from many of the ultimate issues on which juries pronounce, permitting regulation of jury verdicts by reference to any inferential gaps between testimony and factual finding. The relaxation of these two requirements awards more inferential freedom to experts, and so their testimony can often reach closer to the heart of the questions that the jury must answer -- especially where they offer an expert opinion. There is also the fear that juries will suspend their critical faculties because overawed by experts' credentials. For both reasons, the law of evidence pays particular attention to decisions about whether expert testimony will be presented to the jury in the first place.