Saturday, August 30, 2003

Expert Batting Averages for the Millennium to Date

It has been another slow news week on the expert evidence front, so news must be manufactured.

What, it may be wondered, are the overall odds, these days, that expert testimony will survive a Daubert challenge in the federal courts? No doubt expert prospects vary widely, depending on the expert's discipline and also, perhaps, on the tribunal. But if we prescind from such variables, and try to come up with a team batting average, how are experts faring as a group?

At Daubert on the Web, statistics are maintained on the rate at which expert testimony in the various federal judicial circuits, and in various fields of expertise, is held admissible or inadmissible, after appeal. The sample comprises all federal appellate decisions, published or unpublished, rendered on or after January 1, 2000. The sample may be skewed (e.g., because it fails to capture cases in which expert testimony is so unproblematically admissible that no appellate issue ever arises). But that skewing may not be intolerable (e.g., because it seems likely that if any serious evidentiary challenge is mounted in district court, it will be raised on appeal too).

From these statistics, an overall admissibility rate can be extracted. As of today, the sample of 475 appellate decisions includes appellate adjudications on the admissibility of 440 expert opinions. (Some appellate decisions don't reach the admissibility issues, and other decisions rule on the opinions of more than one expert.)

Of the 440 expert opinions on which appellate decision was rendered, the district courts admitted the testimony on 248 occasions, and denied it on 192. So, before appellate dispositions are taken into account, the generic expert batting average in federal court, in this sample, is 248/440, or .564.

Appellate review changes the outcome in about 15% of all cases. That is, approximately 85% of all district court Daubert rulings from which appeal is taken are affirmed, and 15% reversed. But appellate dispositions, important as they may be in individual cases, apparently do not do much to alter the overall averages. Of the 440 appellate rulings on expert opinions, district court decisions to admit the testimony were affirmed on 216 occasions, and district court decisions excluding the testimony were reversed on 35 occasions. Thus, after appeal, the expert's testimony was held admissible (or, at least, not inadmissible) in 251 instances, for a batting average of 251/440 = .570.

That figure, however, paints an unduly optimistic picture for proponents of expert evidence in civil cases, and an unduly pessimistic one for criminal prosecutors, because there is a wide disparity in admissibility rates as between civil and criminal trials. Taken as a group, law enforcement experts and forensic witnesses boast a staggering admissibility rate, after appeal, of 93/113 = .823, and decisions involving their testimony make up roughly a quarter of the overall sample.

If the criminological and forensic experts are excluded from the sample, then the overall expert batting average (after appeal) drops to 158/327 = .483.

By way of comparison, in 1913 (his best year), Jake Daubert batted .350 playing for the Cincinnati Reds. Or, if you prefer, you can tell your experts that their odds match up pretty well with the lifetime slugging percentage of Yogi Berra.

What should be made of the fact that an expert's odds of surviving a Daubert challenge in a civil case are approximately 50/50? Cynics might hypothesize that because the rules governing admissibility nowadays are so vague, flaccid, and manipulable, outcomes will naturally tend to approximate the results that would be produced by flipping coins. And there may be some truth in such an explanation.

But it may also be the result toward which a rational system would tend. Here it would be interesting to hear commentary from economists and game theorists. Your humble investigator is neither of those things, but it may be speculated that litigants tend to push expert testimony, or challenges thereto, as far as they judge the rules to permit, so that the battle is usually at the margin of admissibility, where the decision might tip either way.

As experts are wont to say, further study is warranted.
Fed. R. Evid. 702: 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.