July 28, 2014

Fight False Equivalency Among Experts

By Dr. Ken Broda-Bahm: 

Not Equal

Consider the expert witness mismatch: One expert represents the common mainstream scientific view, while the other expert is there to support a theory that lies on the far side of the credibility spectrum, and may have just barely survived a Daubert challenge. Yet what jurors see is an equivalency. One expert is on one side, and one is on the other. The views of a wackier expert may represent one percent or less of the relevant scientific community, but in the courtroom, that expert rises to 50 percent of what is shared. The comedian John Oliver noted this problem in a recent segment of HBO’s Last Week Tonight. Suggesting that the media set up a false parity when pitting one scientist who believes in man-made climate change against one scientist who discounts it, Oliver’s solution is to represent the true proportions. So he invites three climate change skeptics to share their views, and then fills the studio with 97 scientists on the other side.

Of course, that solution isn’t available to litigators. In court, that effort to represent the proportional weight of opinion would be shot down faster than the other side can say “cumulative.” The general problem is referred to as the fallacy of “false equivalency,” and this democratic notion that there are always “two sides to the story” can end up giving an unearned advantage to a side that is far less reflective of consensus and evidence. Various conspiracy theories benefit from that treatment, as do more mainstream topics such as the perceived health risks of immunizations. In these public discussions, as well as in the courtroom, there needs to be a way to cut through the false equivalency and emphasize what is more fully supported based on the weight of evidence and expert opinion.

When the Comparison “Straightens” the Lopsided

The cover of a recent New York Times featured two photographs side by side, both focused on the consequences of the current conflict in Gaza. One showed a Palestinian funeral, and the other showed an Israeli funeral. Similar in composition, the photos linked the two flag-draped coffins and two families in grief. The message of shared suffering, however, belied the facts on the ground: When that cover ran, the Palestinian death was one of hundreds, while the Israeli death was literally the first such casualty in the conflict.

A recent piece in the science blog Skeptical Raptor, discusses a number of problems with the media’s tendency to simply match one view with another, creating the impression that the two must be comparable. On issues such as anthropogenic climate change (ACC), anti-vaccine views, evolution, the age of the earth, and the causal link between HIV and AIDS, the parity in the comparison creates a misunderstanding regarding the quality of arguments on each side. “They’ll have one talking head, usually a scientist who is trying to present nuanced data, usually uncomfortable with public ‘debate,’ going up against a photogenic, possibly a scientist (but in a field totally unrelated to climate studies), who uses logical fallacies and manipulated data to make a point. And the viewer thinks that half the world’s scientists are equally split between both sides of the ‘debate’ regarding ACC.”

The British Medical Journal also weighed in on the manufactured controversy over vaccines: “The media’s insistence on giving equal weight to both the views of the anti-vaccine camp and to the overwhelming body of scientific evidence…made people think that scientists themselves were divided over the safety of the vaccine, when they were not.”

That potential misimpression exists in court as well. The existence of two conflicting experts, both with roughly equal time and comparable attention in direct and cross-examination, can also create the appearance of a more even-handed debate than reality would support.

Correct the Misimpression of Parity

At a scientific level, you want to convey that your expert represents the well-supported mainstream while the other expert is the oddball. So how do you do that? How do you give the jury a reason to trust your expert testimony more, instead of seeing it as just one of two equally valid scientific views? Other than the general (and good) advice to “Be the Better Teacher” in court, I have a few other ideas for breaking through the false equivalency. 

Treat Opinions As Process Not Product

The problem of false equivalency is most acute when expert evidence is presented as a product the expert is offering instead of a process the jurors go through. The ‘product’ view doesn’t distinguish one expert from another, since both experts will be far more qualified than the average juror, and both will come with the implied stamp of approval from the court. Instead of framing the expert testimony as simply an argument from authority, frame it as a way for jurors to explore and buttress their own conclusions. Instead of the implied message of, “I’m an expert, trust me,” go for an implied message of “Let me show you we can work through this together.” With that approach, fact finders don’t just trust testimony because an expert says so. They trust testimony because they trust their own ability to follow and to verify that conclusion.

Focus on Weight of Evidence

The rules against cumulative presentation of evidence are expressly designed to prevent one advocate from simply “outweighing” another with testimony. Still, within the testimony itself, experts should not be shy about sharing what they know about the scientific consensus that supports their conclusions. In a recent post on SciDev.Net, University of Wisconsin-Madison professor Sharon Dunwoody discusses the problem of false equivalence in science reporting, and the fact that reporting on conflicts in scientific opinion leads to the often inaccurate view that “no one really knows.” Instead of encouraging journalists to simply pick a side, she argues that they should accurately report on the weight of evidence. “With this approach a reporter would ascertain not which truth claim is most likely to be valid,” she argues, “but which has garnered the most support from the scientists qualified to vet it.” Experts can convey the same weight of evidence in reports and on the stand.

Capitalize on Overlap

We are used to thinking that an individual expert’s opinion stands or falls based on the quality of their testimony alone. But particularly on complex cases with many experts, those on one side can do much to help each other. Granted, no two experts will have exactly the same background or scope of testimony, but there will often be some overlap. In a chemical crop damage case I worked on awhile back, for example, we had a number of interrelated experts — an atmospheric dispersal expert, a soil scientist, a hydrologist, a plant biologist, and a crop market expert – who together were able to document the harms all the way from the errant chemical cloud to the marketplace. They each covered their own step, but there was also enough overlap in expertise and scope of testimony that they were able to endorse at least a part of other experts’ testimony. That natural overlap helped to convey a sense of team consensus, and provided a great alternative to the “expert on an island” who doesn’t know or care what the other experts are saying.

The false equivalency of journalism is a by-product of the media’s desire to cover all sides. Similarly, the false equivalency of law is due to a commitment to procedural fairness. In both cases, the principle is a good one. But in litigation and particularly in the expert witness category, it is dangerous to risk leaving jurors with an “Oh well, everyone has their own opinion” mindset. Winning the expert battle requires clarity, contrast, and most of all, good teaching. 

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Other Posts on Expert Witness Testimony:  

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