Koch, C. M., & Devine, D. J. (1999). Effects of reasonable doubt and inclusion of a lesser charge on jury verdicts. Law and Human Behavior, 23, 653-674.
The impact of two procedural factors on jury verdicts was assessed in a mock jury study: (1) definition of the term “reasonable doubt” and (2) inclusion of a “lesser” charge against the defendant in addition to a primary charge. Mock juries of 4-7 persons read an edited transcript from a real murder trial and deliberated to a unanimous verdict. Juries with the option to convict on a lesser charge produced more overall convictions than juries receiving only the primary charge, but only when “reasonable doubt” was undefined. Conversely, more murder convictions resulted when the reasonable doubt criterion was defined in relation to being “firmly convinced” of the defendant’s guilt. Parallel analyses of the effects of these two procedural factors on individual juror predeliberation verdict preferences differed in several important ways, highlighting the need for group-level research on juries. Implications, limitations, and a preliminary integrated model of jury decision making are discussed. Definition of “reasonable doubt” interacted with option to convict on lesser charge. No variation in conviction rate across conditions when juries received “firmly convinced” definition of reasonable doubt; undefined reasonable doubt led to higher conviction rate when lesser charge available but lower rate when lesser charge unavailable. More murder convictions with “firmly convinced” definition.