Monday, June 6, 2016

Proposed Uniform Language for Forensic Toxicology

The first document listed in the announcement of "Uniform Language" (UL) documents for forensic science is the Department of Justice Proposed Uniform Language for Testimony and Reports for the Forensic Toxicology Discipline.  At first glance, it seems rather bland, but if the document truly demarcates the range of the "acceptable range of opinions" that DoJ toxicologists may provide, it is impoverished.

For example, the Supporting Documentation observes that "[a]n examiner may be asked if certain symptoms are consistent with those caused by a particular drug," but for decades, forensic scientists, statisticians, lawyers, and psychologists have complained that "consistent with" testimony is vacuous. Evidence usually is consistent with more than one hypothesis. Drowsiness is consistent with ingestion of barbituates, but it also is consistent with lack of sleep. For the symptoms to be probative of some hypothesis, alternative hypotheses must be considered. Diagnosticity depends on the probability of the symptoms under all the hypotheses.

The proposed uniform language obscures this fundamental concept. For example, the UL document provides that an "examiner may ... state that a reported blood concentration is within the therapeutic range, toxic range, or consistent with reported fatal concentrations" and "that a drug or poison found in a hair specimen is consistent with exposure (either ingestion or environmental) to the drug or poison." If a measured concentration falls into the range within which a poison has killed someone in the past, the "blood concentration" (more precisely, the concentration of the poison) would be "consistent with reported fatal concentrations." But it may be that this "fatal concentration" is rarely fatal and is "consistent with" an alternative cause of death. Surely, a toxicologist should be permitted to say as much "based on data published in peer reviewed literature or other authoritative sources."

At the other pole, suppose the concentration is even higher than any fatal dose ever reported. The toxicologist should not be limited to the uniform language. In this situation (and in some less extreme ones), an expert can give a more powerful, useful, and scientifically accurate opinion than "consistent with."

The UL also (inelegantly) cautions that "[a]n examiner may not report or state an opinion that suggests his/her interpretation of the effects of a drug or poison can be specified to the individual whose sample was tested." Does this mean that the toxicologist can say "the defendant had a blood alcohol level [BAC] that indicates intoxication" but cannot say that "the defendant had a blood alcohol level that indicates she was intoxicated"? Both opinions express (or should express) the same idea — that the measured BAC is more probable when the defendant is intoxicated than when the defendant is not intoxicated. (If this statement about probabilities does not hold, then the BAC does not support the hypothesis of intoxication and hence does not indicate intoxication.)

The UL document first suggests that the toxicologist can only speak of "the average human." Then it redefines the average human to be someone exactly like the defendant in our example:
An examiner may report and/or state his/her opinion as to the effects of drugs or poisons on the average human. This opinion should be based on the facts of the case, medical information about the individual that the specimens were collected from (e.g., weight, height, disease state, age), current published studies, and/or the examiner’s training in the fields of pharmacology, physiology, pathology, clinical chemistry, and/or toxicology.
So the examiner must use all "facts of the case" and all the anatomical and physiological variables specific to the defendant but must not say that the opinion pertains to the defendant? Even if the toxicologist hews to this line, what happens when defense counsel asks the expert whether focusing on the defendant by using all the information about the case exceeds the admonition to confine the testimony and reporting to "the average human"? The phrasing in this paragraph needs refinement if not rethinking.

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