An Empirical Method for Harmless Error
D. Alex Winkelman, David V. Yokum, Lisette C. Cole, Shelby C. Thompson & Christopher T. Robertson. Trials are often imperfect. When inadmissible evidence is introduced or the jury is incorrectly instructed, judges must determine whether the error was prejudicial or merely harmless. In making that assessment, judges resort to speculation about the counterfactual question of whether the error changed the outcome, compared to the decision of a properly informed and instructed jury. These decisions are likely colored by confirmation and status quo biases, along with “mental contamination” of the error itself. Even when appellate judges perform these analyses accurately, their decisions appear conclusory. Scholars and judges have roundly criticized this doctrine, but no solution has emerged. We developed and piloted an unbiased and transparent method for making harmless error determinations, using randomized experiments with simulated jurors. To pilot this method on…