By Victor E. Schwartz, co-chair of Shook, Hardy & Bacon L.L.P.’s Washington, D.C.-based Public Policy Group, and Christopher E. Appel, Of Counsel in Shook, Hardy & Bacon L.L.P.’s Public Policy Group.

Recent verdicts by several California juries in lawsuits by plaintiffs alleging they developed cancer from exposure to glyphosate, the active ingredient in the widely used herbicide Roundup®, highlight a recurring problem in the civil justice system with respect to the use of “expert” scientific evidence: the post hoc ergo propter hoc fallacy.

This fallacy, which is observable in many aspects of daily life, presumes that if one thing follows something else, that first thing must have caused the second thing. For example, a person who develops a fever after eating leftovers the night before might erroneously assume the two are related. A person who lets a friend use her cell phone to make a call and notices the returned phone is not working properly might erroneously assume the friend is to blame. Many superstitions, for instance a black cat crossing a person’s path providing a warning of a subsequently occurring accident or mishap, provide further examples of the post hoc fallacy.