I have followed with interest the legal issues surrounding expert scientific testimony in the courtroom. This is one of those topics that should be well known, but is generally not known outside of legal circles or those who have been at the wrong end of a liability suit.

It seems like a no-brainer that generally the public would want good science in the courtroom, and it is easy to understand the miscarriage of justice that would result from junk science. In a way science in the courtroom is a form of applied science – actual decisions have to be made, even when the science is inconclusive. In practice the line between solid science and speculative opinion is not stark, and it is that line that has been the focus of rules and precedent regarding expert testimony.

A recent court decision on a case involving manganese exposure and Parkinson’s disease seems to represent a positive trend in dealing with expert testimony. The case involves Jeff Tamraz who alleged that exposure to manganese through welding led to his Parkinsonism – a family of neurological disorders. Tamraz and his wife were awarded 20.5 million dollars by a jury, who decided against the five companies being sued. Those companies appealed the decision, and an appelate judge just set aside the judgment on the basis that the court in the case overstepped their bounds and violated Federal Rule 702 pertaining to expert testimony.

Rule 702 was amended in 2000 to include:

If scientific, technical, or other specialized knowledge will assist the trier of fact 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.

This amendment was meant to clarify the Daubert precedent, set in 1993. Actually the Daubert rule often refers to several precedent cases that together establish that judges can act as gatekeepers of expert testimony admissibility, that expert testimony needs to be based on relevant science, and that even not-strictly scientific areas of expertise apply.

But Daubert was often criticized as being vague, and so Rule702 was amended to make it more clear – that expert testimony has to be based on actual evidence. The recent ruling, apparently, is an important decision because it affirms the new and improved Rule 702 by excluding expert testimony because it crossed over the line from expert opinion to speculation. From reading various legal blogs it seems that this case is likely to have important implications for other similar cases.

The facts of this particular case are interesting from a neurological point of view. Tamraz has Parkinsonism – that much is not in dispute. Parkinsonism is a type of neurological disorder involving the basal ganglia, part of the brain that modifies movement to make it smooth and responsive. In Parkinsonism the feedback loop is disrupted, resulting in tremors, decreased movement, and impaired gait and balance.

The most common type of Parkinsonism is Parkinson’s disease, which is a degenerative disorder of unclear cause. It is, however, treatable with medication (improves symptoms but does not alter the course of the disease.

Manganism is caused by manganese toxicity and results in the symptoms above. However, there are differences with Parkinson’s disease. The symptoms are more symmetrical right and left, and the resulting gait has some specific features and has been described as a cock walk.

Apparently Tamraz clinically has a picture more like Parkinson’s disease and not like manganism. However, his neurologist speculated that perhaps he was predisposed to developing Parkinson’s disease and manganese exposure, while not sufficient to cause manganism, triggered Parkinson’s disease.

This is a fine theory, but it is simply not based upon establish scientific facts. And that is the precise basis of the appelate judge’s decision – the expert testimony was too speculative to be admissible.

I could not help thinking of all the vaccine-related cases that similarly are based upon speculation about mercury and autism. Anti-vaccine activists once claimed (and some still cling to this notion) that autism is mercury toxicity. That hypothesis has been rejected by scientific evidence. Autism, in fact, does not resemble mercury toxicity, and people with autism are not mercury toxic. So the antivaccinationists retreated to a more speculative position – that mercury triggers autism in a genetically susceptible subpopulation. This sounds strangely similar to the Tamraz theory above.

It is good to see that speculative theories about environmental triggers, lacking supportive evidence, do not pass the amended Rule 702. This may be an important precedent indeed.