UCLA Criminal Justice Law Review

Judgments about the harmfulness of trial errors have profound consequences for defendants, the criminal justice system, and the public. Judges are expected to assess harm accurately, but they cannot hear directly from jurors and may only speculate about the difference a trial error made. Even experienced judges have a hard time predicting what jurors think and what juries will do. Fortunately, scientific principles and research can assist judges in conducting harmless error analysis. This Article offers a framework for testing claims about the harmfulness oftrial errors. It specifies the prosecution’s burden to prove a trial error was harmless on direct appeal as well as the defendant’s burden to prove a trial error was harmful in post-conviction proceedings. Hypotheses about the harmfulness of errors can be visualized and tested rigorously. Scientific analysis of trial errors can help courts assess the harmfulness of trial errors more accurately, efficiently, and confidently.