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It would be a remarkable business plan to win product liability lawsuits.  Locate a potential plaintiff who has the disease and who also has had some – any – exposure to the product or toxic substance.  That’s it.  You win.  No need to worry about the other side ruling out the product or substance as a cause.  They can’t.  Once there’s exposure, it’s a cause.  No need to worry about your side ruling out other potential causes of the disease.  That doesn’t matter.  The plaintiff has the disease, and the plaintiff was exposed: you win.
It’s a plaintiffs’ lawyer’s dream.  Case specific facts for the most part become irrelevant.  You don’t have to worry about alternative causes, other risk factors or evidence of low exposure.  You don’t need to sweat the science.  Specific causation expert opinions are simple and almost unassailable.  No worrying your way through tense depositions dissecting your expert’s opinions on the necessary levels of exposure or the effect of exposure at low levels.  It just doesn’t matter.  Any exposure is enough exposure.  You win.
Of course, this dream business plan would be a nightmare for defendants, and the courts.  Fortunately, all this remains in the world of dreams and nightmares.  Because it isn’t reality.
The decision in Schultz v. Glidden Co., No. 08-C-919, 2012 U.S. Dist. LEXIS 38163 (E.D. Wi. Mar. 20, 2002), is a good example of this.  In Schulz, the plaintiff claimed that her deceased husband got Acute Myeloid Leukemia (“AML”) from exposure to the defendants’ products, which contained benzene.  The plaintiff had a case-specific expert who opined that the husband had been exposed to 20 ppm-years of benzene, and the defense had an expert who opined that almost twice that exposure was necessary to cause AML.  Id. at *6-7.  Those types of opinions are fairly standard in product liability litigation.
But what makes this case interesting is that neither of those opinions really mattered because the plaintiff offered a general causation expert who said that any non-trivial exposure to benzene was enough to cause the deceased’s AML:
When no safe threshold of exposure to a carcinogen has been established, this means that each and every exposure to the chemical will increase the risk of development of the types of cancer that the carcinogen is capable of causing.  To the extent that an individual has developed a type of cancer caused by the carcinogen in question, then any non-trivial exposure to that carcinogen during a time frame consistent with the range of latency periods with the disease should be considered as a probable substantial factor that contributed to the development of the individual’s cancer.
Id. at *8-9.  In other words, it didn’t matter whether the deceased had been exposed to 24 ppm-years of benzene, or 5, or 100.  Any non-negligible, non-trivial exposure was enough. 
That’s not all.  The expert also opined that, once you find this exposure to benzene, you cannot exclude benzene as a possible cause of the deceased’s AML.  Not ever:
To the extent a known risk factor for a particular type of cancer has been identified in an individual who has developed that form of cancer, exclusion of that risk factor as one of the probable causes contributing to the cancer is not scientifically possible.
Id. at *9.  So, not only is any non-trivial exposure enough, but once you’ve got it you can’t rule it out.
There’s still more.  According to this expert, even if there were sufficient and present alternative causes of the deceased’s AML, that wouldn’t matter.  Alternative causes “in no way undermine[]”that benzene played a “substantial role in the development” of the deceased’s AML.  Id. at *13.   
Well, that’s a non-trivial amount to swallow.  Any non-negligible exposure to benzene and the case is essentially over.  Benzene becomes a cause that cannot be eliminated.  None of the other causes – even if present – can change that.  No further evidence or explanations are needed.  That’s a bad place for the defense to be.  
Fortunately – science, Daubert and common sense to the rescue.  The Schultz court found plenty of reasoning in previous benzene cases that the science just doesn’t work this way.  It doesn’t support this “no-threshold” or “one-hit” theory of causation:
The theory that any amount of exposure more than negligible should be considered substantial risk factor for AML flies in the face of the scientific literature reviewed and other expert testimony in this case that there is a threshold or dose below which you do not see a statistically significant risk of developing AML.  Even though benzene has been shown to cause AML, it is too difficult a leap to allow testimony that says any amount of exposure . . . to this toxin can cause AML and caused AML in the plaintiff.
Id. at *9-10 (quoting Henricksen v. ConocoPhillips Co., 605 F. Supp. 2d 1142, 1166 (E.D. Wash. 2009); citing Baker v. Chevron USA, Inc., 680 F. Supp. 2d 865, 878 n.9 (S.D. Ohio 2010) (“The ‘one-hit’ or ‘no threshold’ theory of causation in which exposure to one molecule of a cancer-causing agent has some finite possibility of causing a genetic mutation leading to cancer is not a reliable theory for causation under Daubert standards.”))
The court also properly found that this “no-threshold” theory of causation fails every Daubert smell test there is: 
The linear non-threshold model cannot be falsified, nor can it be validated.  To the extent that it has been subjected to peer review and publication, it has been rejected by the overwhelming majority of the scientific community. It has no known or potential rate of error.  It is merely a hypothesis.
Id. at *10-11 (quoting Whiting v. Bos. Edison Co., 891 F. Supp. 12, 25 (D. Mass. 1995); citing Sutera v. Perrier Grp. of Am., Inc., 986 F. Supp. 655, 666 (D. Mass. 1997) (“There is no scientific evidence that the linear no-safe threshold analysis is an acceptable scientific technique used by experts in determining causation in an individual instance”)).
The Schulz court was on a roll.  Not only did the non-threshold test fall in the face of science and Daubert, the expert’s opinion that he didn’t need to address or disprove other alternative causes was also a Daubert loser: “if an expert utterly fails to consider alternative causes or fails to offer an explanation for why the proffered alternative cause was not the sole cause, a district court is justified in excluding the expert’s testimony.”  Id. at *12.  This comports with our common sense: if something else caused the AML, then it wasn’t the benzene.  This isn’t reasoning that can be dispensed with simply because it makes things more complicated or more difficult for the plaintiff or the court.  It must be dealt with head on and, if not, plaintiff’s claim must fall.

Science in the courtroom isn’t, or shouldn’t be, a process that can be gamed. The idea is not to put forward expert opinions that will work for every case and that resist testing and evaluation. It is in fact the opposite. The science must be the science, not a strategy. The nature of science is testing, probing and questioning, not insulation from these things. The no-threshold, no alternative cause approach defies all of this.

So, while these types of expert opinions may seem like a dream to some plaintiff’s attorneys, in reality they’re straight-up losers. The Schulz court granted summary judgment to the defendants and dismissed the case.