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Diverging from the shadows: explaining individual deviation from plea bargaining in the “shadow of the trial”

Abstract

Objectives

The “shadow of the trial” (SOT) theory posits that plea decisions result from mathematical predictions of probability of conviction (POC) at trial and potential trial sentence (TS). Tests of the SOT model often find support in the aggregate, but not at the individual level. This study examines the factors that account for adherence to, or deviation from, the SOT model, such as mathematical competence, a factor not previously examined in tests of the SOT model.

Methods

Participants were randomly assigned to one of nine conditions corresponding to manipulations of probability of conviction (10%, 50%, 90%) and potential trial sentence (5, 15, 25 months). After reading a case description, participants were asked whether they would accept a plea offer and how much time in jail they would be willing to spend; a subset of participants was offered a counter plea offer. Participants then answered questions assessing numeracy and about their legal opinions and personal characteristics.

Results

Results showed that probability of conviction, but not trial sentence, influenced shadow model adherence. Participants assigned to 50% and 90% POC conditions were significantly less likely to deviate from the SOT model than participants assigned to 10% conditions. This effect did not interact with TS. Additionally, the odds of fitting the SOT model increased significantly as participants’ numeracy scores increased.

Conclusions

Our results raise questions about the validity of the SOT model at low POCs and challenge its assumption that defendants are capable of conducting the mathematical calculations required to fit the model.

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Fig. 1
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Notes

  1. 1.

    This question presented the participant with three options: (1) accept a plea offer if it is the value they specified or lower, (2) accept the plea offer even if it higher than the value they specified, or (3) reject the plea offer regardless of the length of the jail sentence. These categories were subsequently collapsed into a dichotomous measure of whether or not the participant was willing to accept a plea offer versus unwilling to accept any plea deal.

  2. 2.

    Note that participants who indicated that they were unwilling to accept a plea deal of any value were coded as deviating from the shadow model regardless of whether they disagreed with their attorney.

  3. 3.

    A post hoc power analysis indicated that our sample size for logistic regression models 1 and 2 was sufficient to detect an odds ratio of 1.68 (power = 0.92), considered equivalent to a Cohen’s d of 0.2 or higher (see Chen et al. 2010).

  4. 4.

    The results of models 1 and 2 remained unchanged when the invalid responses were included.

  5. 5.

    Estimated statistical power to detect an odds ratio of 1.68 decreased to 0.78 for model 3 due to sample attrition. This is a power level slightly lower than the convention of .80 proposed by Cohen (1992).

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Acknowledgments

We would like to thank Tina Zottoli and Jennifer Bartlett for sharing their work with us and for their continued communication and insight throughout the course of this study.

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Correspondence to Kevin Petersen.

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Petersen, K., Redlich, A.D. & Norris, R.J. Diverging from the shadows: explaining individual deviation from plea bargaining in the “shadow of the trial”. J Exp Criminol (2020). https://doi.org/10.1007/s11292-020-09449-4

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Keywords

  • Shadow of the trial
  • Plea bargaining
  • Guilty pleas
  • Legal decision-making
  • Numeracy
  • Criminal justice