In this third and last installment of our three-part series examining the type of deposition questioning that can derail your opponent’s expert and set up a successful Daubert challenge, we will look at Daubert’s insistence that the expert’s opinions be based on “reliable methodology” before opinions can be presented to the jury.

What exactly does a reliable methodology under Daubert mean? Essentially, it requires that the expert’s opinions be based on information gathered in the same manner as a scientist would undertake before he or she reaches a conclusion about the design of the product at issue. The distinction is between using sound scientific procedures as opposed to unsupported speculation to develop a hypothesis, analyze and test against it, and reach a conclusion.

Careful and targeted questioning of the expert often can establish that the expert’s opinions are indeed the product of nothing more than guesswork and conjecture – the very ipse dixit approach against which Daubert and its progeny warned and that the Federal Rules, when properly enforced by the court exercising its “gatekeeping” function, should disallow. Fortunately, Daubert and its progeny have given us extensive guidance as to the types of questions to ask the expert to establish the expert’s lack of sound methodology. They involve concepts such as testing, “peer review,” rates of error, the existence of standards, “general acceptance” and other well-defined criteria. Let’s look at some of them.

Assume for the sake of this example that a plaintiff’s expert has opined in a report that your client’s Widget-making machine was defectively designed because it lacked a guard over its cutting implement. That hypothesis, like all hypotheses, could theoretically be tested, but has the expert bothered to do so? For example, has the expert actually designed and placed a guard over the Widget-making machine to see if, under real working conditions, it actually cuts down on the frequency of accidents without reducing the machine’s overall functionality and utility?

“Peer review” is the process by which a scholarly work (such as a paper or a research proposal) is vetted by a group of experts in the same field to make sure it meets the acknowledged and accepted standards in the field before it is published or generally accepted. Why should the plaintiff’s expert’s opinion (i.e., scholarly work) be any different, or immune to this level of scrutiny? Under Daubert, it isn’t. For that reason, effective questioning of the expert often will establish that his theory of defect – in our imagined scenario, the lack of a guard over the Widget-making machine’s cutting implement – has never been published anywhere other than in a series of the expert’s reports he issued in prior lawsuits. Therefore, by definition, the theory of design defect the expert is advancing in your case has never been offered for commentary to other experts in the same field. Once this fact is established, the plaintiff’s expert is nothing more than a lone wolf; his theory of design defect has never been checked for scientific soundness and has never become generally accepted by the community of similarly situated scientists.

Real scientists employ the scientific method to develop a hypothesis, test against it and then reach a conclusion about the soundness of the hypothesis. Real scientists then publish their theory in trade journals and give speeches about it at industry or academic gatherings. In this way, the expert’s proposed testimony grows naturally and directly out of healthy and impartial scientific curiosity. If targeted questioning establishes that the expert has never published the theory of defect in anything but the reports that were prepared within the context of litigation, then the expert’s opinions become nothing more than the product of advocacy instead of the product of real scientific inquiry.

Will the guard over the Widget-making machine’s cutting implement stop all accidents, or only some of them? If questioning establishes that there remains a fair modicum of Widget-machine accidents that would happen even with a guard over the cutting implement, then it also has established that there is a certain amount of “known or potential error” in the plaintiff’s expert’s hypothesis. Stated otherwise, the expert’s proffered design is no panacea.

Similarly, has the expert accounted for other possible explanations for the accident? What if the plaintiff was hurt simply because he or she was under the influence of alcohol? What if the Widget-making machine originally had a guard over its cutting implement, but the guard had been removed? Real scientists, using a legitimate methodology, strive to explain away all other possibilities for an accident’s occurrence.

Effective questioning of the expert also can establish that the expert can cite no known published standard – voluntary or mandatory; governmental or private – to support his theory. In our fictional example, effective questioning can show that no body of experts in the field, who were otherwise charged with the deliberative task of developing standards over a period of months or years for the safe design and use of Widget-making machines, had ever advanced the notion that a guard over the cutting implement was necessary to make the machine “safe.” Again, the plaintiff’s expert looks more and more like the lone wolf − rather than a reasonable scientist.

In a case in which the expert advanced an opinion that your client’s product was missing an important warning, had the expert actually developed a proposed warning for the product? That is, has the expert actually written the verbiage and determined the warning’s size and shape, the font size and correct “signal” word? Has he tested the proposed warning for “understandability” and its effect on the reader? Will the proposed warning actually work to change the product user’s behavior and prevent an accident? Without such development and testing, the expert’s opinions in this area is speculative at best.

Lastly, effective questioning of the expert should ask whether there is a causal link between the opinion and the facts of the case; that is, as Daubert and its progeny put it, whether the opinion actually “fits” the facts of the case. If questioning of the plaintiff’s expert establishes that the existence of a guard over the Widget-making machine’s cutting implement would have made no difference – perhaps the facts show that the plaintiff intentionally reached into the area of the cutting implement to clear a jam and thus the existence of a guard would not have prevented the accident – then the plaintiff’s expert’s opinion and proffered alternative design, though interesting, arguably proves nothing.

The ways to question a supposed expert’s methodology is limited only by one’s imagination. This article suggests some areas of attack. With effective questioning, your opponent’s expert will look less like an independent and impartial scientist and more like the proverbial “hired gun” who will advance any opinion so long as an attorney is willing to pay the required hourly rate.