How a “Reasonable Doubt” Instruction Affects Decisions of Guilt

Abstract

Jurors are instructed to render a guilty verdict if they feel the defendant is guilty beyond a reasonable doubt. The jury is often told that this does not mean an absolute certainty of guilt and that even if it were possible to imagine a scenario in which the defendant is innocent, a guilty verdict may still be appropriate. Here, participants read a case summary. They were either told to say that the defendant was guilty if they believed in guilt beyond a reasonable doubt or were given more detailed instruction stressing that they did not have to be absolutely certain of guilt to give a guilty verdict. In Experiment 1, participants provided “think-aloud” protocols. Content analysis revealed that those who were given this instruction often used the phrase reasonable doubt to justify their guilty verdicts by saying that although they were not certain of the defendant's guilt, their belief exceeded the reasonable doubt threshold. None of the participants in the control group did this. Experiment 2 was designed to test if the instruction affected belief in guilt and the reasonable doubt threshold quantitatively. The instruction affected both people's belief in guilt and the threshold that they used to define reasonable doubt. The implied values for reasonable doubt were 63% for those who received the instruction and 77% for the control group. Implications for jury decision making are discussed.