[Cross-posted at the Volokh Conspiracy]
I'm working on a paper on the admissibility of expert testimony, and I've noticed a disturbing trend: courts that want to admit questionable expert testimony frequently cite permissive-sounding language from the 1993 Supreme Court Daubert opinion. Daubert was indeed a rather ambiguous opinion, and could indeed provide comfort to judges who want to shirk their "gatekeeper" role.
The problem, however, is that Daubert (and for that matter, its stricter, but still occasionally ambiguous progeny, Joiner and Kumho Tire) is not the governing rule for the admissibility of expert testimony. In 2000, amended Federal Rule of Evidence went into effect. The amended rule was intended to codify the "Daubert trilogy", but wound up containing some stricter language than the Daubert trilogy itself has: "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, if (1) the testimony is based upon sufficient facts or data, (2) the testimony is the product of reliable principles and methods, and (3) the witness has applied the principles and methods reliably to the facts of the case."
Thus, for example, while Kumho Tire suggested that some experts can simply rely on their experience to justify their conclusions, amended Rule 702 requires that the expert be able to DEMONSTRATE that he applied his experience reliably to the facts of the case. This may be impossible in many cases, which is very problematic, but it's equally problematic for a partisan, paid, experience-based expert to be able to testify simply based on his say-so, with no real hope of effective cross-examination. (How would you cross-examine the Kumho Tire Court's example, the perfume-tester, who claims to be able to distinguish among hundreds of perfumes via one sniff? Even if his sniffing is generally reliable, how do you know whether he's correct in this particular case, or is either just wrong or shading his testimony? And how is it helpful to the jury to have two equally qualified perfume-testers, one paid for by each side, both swearing based on nothing more than their say-so that the perfume is, respectively, Chanel or Gorgio?) (I have an idea how to rescue experience-based testimony from Rule 702 oblivion, but I'll save that for another time.)
To take another example, way too many courts have relied on language from the trilogy in admitting phony "differential diagnosis" testimony on causation that in fact constitutes nothing more than "post hoc ergo propter hoc" reasoning. Allowing an expert to testify that exposure to substance X caused injury Y simply because the expert can't identify any other cause, and in the absence of any proof that substance X CAN cause injury Y, is not exactly reliable principles and methods being applied reliably to the facts of the case. It's more like, in many instances, allowing paid hired guns to speculate wildly to a conclusion mandated not by science but by the necessity of supporting a plaintiff's causation theory.
In short, it is obviously illegitimate for federal courts to rely on language from Daubert, or even Joiner or Kumho Tire--each of which interpreted OLD Rule 702, when there is contradictory, stricter language from NEW Rule 702.
I'd welcome examples to add to my collection of courts privileging language in the Daubert trilogy over the text of new Rule 702.