Expert testimony and substance-themed mitigation in capital case sentencing

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University of Alabama Libraries

The present study explored how jurors utilize biopsychosocial variables during the sentencing phase of a capital trial.  According to literature, certain mitigating factors, like substance abuse, cause a "backfire effect."  This means that contrary to the defense's intentions, jurors considered the information more aggravating than mitigating.  Previous studies of biopsychosocial mitigation have neglected the impact of expert testimony on juror decision-making.  Ideally, an expert imparts knowledge so jurors are more informed in their sentencing choice.  However, such testimony may exacerbate the “backfire effect” by underscoring unfavorable qualities of the defendant. Hypotheses anticipated participants (mock jurors) exposed to expert testimony regarding a defendant’s substance abuse would be more likely to choose the death penalty. Further, it was anticipated this effect would be greater for mock jurors displaying problematic drinking patterns. Results revealed a significant main effect of expert testimony such that mock jurors exposed to testimony were significantly less likely to choose the death penalty, regardless of whether the defendant abused substances. Upon further investigation, the significant effect of expert testimony only held true for college student participants. These results highlight the importance of a two-step process of data analysis in juror decision-making studies using college student samples. Specifically, significant effects should be confirmed within a more venire-representative sample before drawing conclusions. Uncovered data also shed more light on the influence of expert testimony during capital cases, as well as the juror characteristics associated with different sentencing decisions for a defendant displaying mental health problems. In addition, data suggested substance-themed mitigation is not necessarily deleterious for the defense. Effective expert testimony may provide a buffer against the backfire effect, especially for jurors with higher levels of achieved education.

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