Rethinking Expert Testimony: The Case for Concurrent Evidence

Expert testimony is often the center of gravity in life sciences and technology disputes because patent, licensing and other commercial cases often turn on specialized scientific or technical questions.

Yet the traditional method of presenting expert testimony—one side presents its expert, the expert is examined and cross-examined and, days later, the opposing expert goes through the same process—is not always well suited to resolving these questions. By the time the second expert addresses a point made by the first, the tribunal is comparing testimony delivered at different times, in response to different questions and sometimes using different terminology or assumptions. And much of what the experts have to say is really not in dispute.

There is another way.

Concurrent expert evidence, sometimes called “hot-tubbing,” brings experts together to address common issues at the same time. Used thoughtfully, it can be very effective in life sciences and technology arbitrations, where experts often agree on the underlying science or technology and disagree only about a few judgments, assumptions or conclusions.

The Problem With Sequential Testimony

The conventional adversarial model emphasizes disagreement: Each expert prepares a report supporting one party’s position, direct examination summarizes that opinion and cross-examination points out weaknesses.

That structure can make two expert opinions appear further apart than they are. Because opposing experts write reports independently, much of what they cover is uncontroversial background. And because lawyers may hesitate to concede that any part of an opposing expert’s report is right, genuine agreement can become obscured, leaving the impression that the experts disagree more broadly than they do.

I have seen this firsthand. In a battery chemistry case, the parties’ experts submitted reports that appeared to present competing technical views. When they addressed the issues together, however, they agreed on virtually everything that mattered about the chemistry and operation of the technology. Their disagreement came down to the quantum physics explaining why the chemistry worked as it did. Identifying that narrow disagreement narrowed what the tribunal had to resolve.

In another case, experts who appeared from their reports to have significant technical disagreements agreed on essentially all relevant technical issues when their positions were examined together. Their ultimate disagreement arose from different application of a contract provision. In other words, the key issue was not within either expert’s area of expertise; it was a question of contract interpretation for the tribunal.

These experiences illustrate a principal advantage of concurrent evidence. What looks like a broad battle between competing experts may involve a single technical disagreement—or one that is not even properly a matter for expert testimony.

With concurrent testimony, the focus for the tribunal switches from “Which expert do I believe?” to “Where do they disagree, and what scientific or technical judgment accounts for the difference?”

What Concurrent Evidence Looks Like

There is no prescribed format; the process should be tailored to the dispute. For example, a tribunal might use conventional examination for some subjects and concurrent evidence for discrete scientific or technical questions. Or it might ask the experts to prepare a joint statement after they exchanged their reports, identifying where they agree and where they disagree and, for each disagreement, explaining why. That statement then sets the agenda for the joint session. Or the tribunal might simply proceed issue by issue.

With both experts sitting side by side, the tribunal can ask each to explain a position on a particular question and, under appropriate controls, to respond directly to the other. A tribunal hearing accomplished scientists or engineers discuss the same experiment, system, dataset or assumption at the same time may learn more than it would from examinations separated by several days.

Why It Works Particularly Well in Complex Scientific and Technology Cases

Life sciences and technology disputes frequently involve complex subjects, but complexity does not mean that every scientific or technical proposition is contested. In fact, one of the most useful questions a tribunal can ask experts is also one of the simplest: What do you agree on?

Molecular biologists may agree on most of the science but disagree about what an experiment demonstrates. Pharmaceutical experts may accept the same data but reach different conclusions about whether a manufacturing deviation affected product quality. Software experts may agree on how a system operates but disagree about one module or a few lines of source code. AI experts may agree on how a model was trained and deployed but disagree about why it produced a particular result.

Isolating that disagreement can transform the tribunal’s understanding. Concurrent evidence changes the dynamic. When experts testify separately, their immediate counterpart is the lawyer asking questions. In a concurrent session, it is another expert in the field, and this can encourage a different kind of precision. An expert may be willing to accept a broad proposition during examination by counsel. That is harder when, moments later, another expert says, “I agree with you up to that point, but the conclusion does not follow because you have assumed X.”

For the tribunal, that exchange may be more valuable than another hour of cross-examination. Suddenly, the dispute has a shape.

Concurrent Evidence Does Not Eliminate Advocacy

Some counsel are wary of concurrent evidence because it appears to surrender control over expert testimony. It need not. Some issues may lend themselves to concurrent testimony while others do not. The choice need not be binary. If credibility is central, or an expert must be confronted with documents or prior statements through cross-examination, sequential testimony may be preferable.

Flexibility is one of arbitration's principal advantages. The procedure should not be an unstructured scientific or technical seminar. The tribunal must actively identify subjects, keep the discussion focused, give each expert a fair opportunity to respond and prevent either from dominating. And counsel must retain the opportunity to examine experts, test assumptions, expose inconsistencies and develop points relevant to their client’s case, even after tribunal questioning.

Arbitration Gives Us the Opportunity to Do Better

Litigation procedures developed over generations; arbitration gives parties and tribunals an opportunity to reconsider those inherited procedures. But for a decision-maker facing a complicated technical record, agreement can be as important as disagreement. Parties can then focus their briefs and examinations on disputed issues.

Once a disagreement is isolated, the tribunal can ask better questions: Is the difference based on competing data? Different assumptions? Different methodologies? Different interpretations of the scientific literature or technical record? Or simply different judgments about what conclusion the evidence permits?

Those are the questions that ultimately matter.

The objective is not simply efficiency, although concurrent testimony can save substantial hearing time. Efficiency does not mean abandoning cross-examination or turning every hearing into a roundtable. It means asking at the outset what process will best help the tribunal understand the dispute.

When experts agree on most of the underlying science or technology, the tribunal should not have to excavate their disagreement from separate mountains of testimony.

Put the experts together. Identify the common ground. Find where their paths diverge.

Then ask why.