Testing the Impact of Criminal Jury Instructions on Verdicts: A Conceptual Replication
117 Columbia L. Rev. Online 22 (2017)
14 Pages Posted: 24 Jul 2016 Last revised: 30 Jul 2017
Date Written: July 23, 2016
The Constitution protects us from criminal conviction unless the state can prove guilt beyond a reasonable doubt. However, many of our nation’s trial courts will conclude their burden of proof instructions by telling jurors not to evaluate the evidence for doubt, but instead “to search for the truth” of what they think really happened.
In our previously published study, we empirically demonstrated that such truth-related language lowers the state’s burden of proof below the constitutionally-guaranteed reasonable doubt standard. In this article, we discuss the results of our new empirical study — a conceptual replication and extension of our previous work.
In our new study, we again found a statistically significant difference in conviction rates between mock jurors who were properly instructed on reasonable doubt, and mock jurors who were instead instructed “to search for the truth.” Additionally, we identified a cognitive link between the truth-related jury instruction and the increased conviction rate.
More specifically, mock jurors who were instructed “to search for the truth” were nearly twice as likely to mistakenly believe they could convict the defendant even if they had a reasonable doubt about his guilt. Further, mock jurors who held this mistaken belief actually voted to convict the defendant at a rate 2.5 times higher than those who correctly understood the burden of proof.
Our original study, our successful replication, and our newly discovered cognitive explanation for juror behavior combine to provide powerful evidence that truth-related language diminishes the constitutionally-mandated burden of proof. Therefore, in order to protect our Due Process rights, courts should immediately remove such truth-related language from their burden of proof jury instructions.
Keywords: Criminal Law, Constitutional Law, Jury Instructions, Burden of Proof, Empirical
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