Juror “Guide” for Roundup Trials?

Michael Stiles
6 min readApr 24, 2019

Considerable media attention has been directed at the so-called Roundup trials in which plaintiffs allege the use of glyphosate formulations such as Roundup caused Non-Hodgkin’s Lymphoma (NHL). The media headlines and accompanying narratives emphasize the plight of the plaintiffs, potential liability for Monsanto/Bayer and attention-getting claims and counter-claims from the trial. However, little notice has been given to the complicated trial process and the multiple factors affecting the ability of jurors to obtain a verdict consistent with the scientific evidence and legal precedents.

Roundup trial testimony heard by jurors is almost exclusively from a broad range of expert scientific and medical witnesses for which judges exercise their “gatekeeper” role pursuant to jurisdiction specific standards. The gatekeeper role determines the adequacy of experts for testifying regarding one or more of the scientific disciplines, but does not evaluate the adequacy of subsequent testimony or referenced studies. Judges may also set limits for testimony or evidence based on the relevancy, adequacy and “fairness” of proposed testimony or subject matter.

Tracking trial evidence is difficult for jurors because specific topics are not logically grouped during the trial. Subject matter evidence from direct and cross examinations of one or more plaintiff’s witnesses may again be addressed several days later with different aspects from defense witnesses’ examinations. Those trials not split into causation and liability phases are further complicated by additional testimony for liability allegations largely based on document interpretations.

Additional factors affecting jurors are derived from the adversarial nature of trials. Both sides emphasize the best aspects of their case and minimize, obscure or are less than forthright regarding weaknesses. The adversarial trial presentations, structural dispersion of evidence and a jury unsophisticated regarding relevant scientific disciplines, legal considerations and attendant psychological pressures (finding a culprit for the cancer and/or sympathy for plaintiff) have a significant potential for distorting jury verdicts. Ultimately, jurors are required to understand, synthesize and weigh specialized aspects for a large body of evidence regarding epidemiology, toxicology, statistics, genetics and various medical specialties, among other disciplines, to arrive at necessary verdicts:

- Did plaintiff prove it is more than likely a glyphosate based formulation (GBF) was a substantial (causation) factor for plaintiff incurring NHL?

- If GBF was a substantial factor, what are the economic liability damages for which plaintiff is entitled and, if applicable, the punitive damages for negligence allegations proven by the plaintiff?

However, the most problematic trial issues relate to the decisions jurors are forced make without appropriate consideration for the scientific and legal significance of evidence and allegations. Jury instructions do not contemplate undisputed scientific truths and associated legal precedents or the scientific context and significance underlying liability allegations.

Alternatives for addressing the inconsistencies of jury trials for complex scientific based cases have been proposed, but none of proposals gained traction for legal, political or practical reasons (1). However, an intermediate step of structuring jury decision making processes may be more plausible; i.e., the establishment of a scientific guide for jurors with a set of “bright-line scientific criteria”. The guidance could provide scientific and legal criteria for the decision process of jurors tailored to the scientific scope and jurisdictional standards of each trial. In effect, bright-line jury criteria would be a lay person’s subset of the criteria used by trial judges and appellate courts.

The presiding judge, ideally with the advice of a scientific advisor, would propose jury bright-line criteria subject to arguments of opposing sides subsequent to pretrial examination of expert witnesses. For example, bright-line scientific criteria for Roundup trials could include:


· Jury subordinate or overall conclusions cannot be obtained from the summation of unreliable or marginally significant studies or a scattering of problematic studies.

· A hazard analysis (alone) normally is not oriented to risk exposures for humans and cannot provide suitable proof of causation for human populations, much less specific plaintiffs. (2)

· Internally valid epidemiological studies with reliable results for human populations cannot be overridden by biologically distant conclusions from animal and mechanistic studies. (3) Alternatively, where internally valid epidemiological studies with reliable results exist, animal and mechanism studies can only support or negate biological plausibility.

· Risk measures from population or epidemiological studies must be adjusted for other confounders, including pesticides, using a valid statistical technique to obtain reliable risk measures for use in forming jury conclusions. Non-adjusted and inappropriately adjusted results (4) cannot be used for forming conclusions. Epidemiological reliable risk measures of less than 2.0 are to be considered as a “less than likely” causal probability. (5)

· Trends among epidemiological studies or meta-analyses do not provide conclusive evidence unless all of the inclusive studies have internal validation and consistent measurements as well as a trend reflecting a causal or non-causal association.

· Jury conclusions for rodent carcinogenic studies should exclude study results which do not show similar effects for directly comparable rodent types and breeds; lack of dose response effects; results within historical controls limits for breed or laboratory or results which have no biological significance.

· Challenging pathology conclusions of animal carcinogenic studies requires contrary pathological evidence be presented for a jury conclusion.

· The reliability of an overall cellular mechanistic or genotoxicity conclusion is dependent upon several factors: use of an overall weight of evidence approach with each category of test type weighted to reflect human relevance, predictive capability and conclusive testing end points; tests are performed in accordance with Organization for Economic Co-operation and Development (OECD) and Good Laboratory Practice (GLP) guidelines; and all relevant and published studies, including those from detailed and peer reviewed papers are included within evaluation. (6)

· Studies with human genotoxic measurements must be compared to study author conclusions, reliability of utilized tests and determination of whether results reflect secondary effects before arriving at jury conclusion.

· A medical differential diagnosis cannot “rule in” GBFs unless the weight of the evidence supports an overall causation for populations. If general causation has been proven, but unknown or idiopathic causes account for more half of cases of the plaintiff’s NHL sub-type, the primary candidate for causation is idiopathic. “Ruling out” idiopathic causation when it is most probable causation would require extraordinary evidence.


· Allegations must be evaluated for subsequent effects on public or scientific opinion. Effects relating to only public opinion or legitimate scientific controversies do not have a liability significance

· Controversies regarding disputes between autonomous organizations and regulatory authorities are legitimate candidates for public and scientific debate and without significance for liability.

· Unless scientific facts derived from primary studies, regulatory and published, are altered or deleted there is no scientific significance attributable to a liability allegation.

· The entire story for an allegation must be evaluated prior to forming a conclusion.

· The absence of confirming evidence for an allegation is speculation and is not relevant for forming conclusions,

Notably, the proposed bright-line juror criteria are related to claims or allegations having varying degrees of speculation and further emphasize the importance of scientific criteria to reduce the number of jury verdicts based on jurors assuming a false scientific and legal significance for speculative evidence. This approach appears applicable to civil trials dependent on scientific based evidence and optimistically, can focus the trial presentations on critical scientific and legal points, help preclude obvious grounds for appeals and improve judicial economies.

(1) Judges, Juries and Scientific Evidence Hans 2008

(2) Classification Schemes for Carcinogenicity Boobis et al, 2016

(3) Getting to Causation in Toxic Torts Bernstein 2008

(4) Sparse Data Bias Greenland et al, 2016

(5) Epidemiological Uncertainty Goldberg 2014

(6) Genotoxicity Expert Panel Review Brunswick et al, 2016 (including referenced guideline papers)