Jury Deliberation and Group Polarization
In a mock jury study, 60 participants are randomly assigned to ten six-person juries. Each jury reads a trial summary with ambiguous evidence: a store security camera shows a man near the register at the time of a theft, but the face is obscured; a cashier identifies the defendant with 70% confidence; the defendant has a prior conviction for shoplifting. Before deliberation, jurors privately indicate guilt on a 1-7 scale. The initial mean is 4.2, with four jurors leaning guilty and two leaning not guilty. After 90 minutes of deliberation, five jurors vote guilty and one votes not guilty; the mean guilt rating rises to 5.6. The researchers conclude that deliberation produces group polarization.
1. Is 'group polarization' the best explanation? What alternative social psychological processes could produce the shift?
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Reasoning: Group polarization is a reasonable description: the jury's initial lean was guilty (4-2), and after discussion the majority grew to 5-1 and the mean rating rose. But the label is not an explanation by itself. Alternatives include informational influence-jurors exchange arguments that shift privately held beliefs-and normative influence-jurors conform to the perceived majority to avoid conflict. The shift could also reflect a leadership effect or the cashier's 70% confidence being overweighted. To distinguish polarization from mere conformity, the study needs private post-deliberation measures and a comparison condition. If private ratings also shift, informational influence is more likely; if only public votes shift, normative pressure is implicated.
2. What design change would help separate informational from normative influence?
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Reasoning: Use anonymous pre- and post-deliberation measures, and manipulate whether participants expect to justify their answers publicly. If the shift persists in private, it is more likely informational; if it appears only when responses are public, normative influence is likely. A second approach is to vary discussion instructions: ask jurors to focus on evidence versus to reach consensus. A third is to include a 'secret ballot' condition and compare it with a show-of-hands condition. Measuring argument quality and the number of novel arguments would also help, because informational influence should track the content of discussion, not just the majority size.
3. If the jury had initially been 4-2 not guilty, would you expect the same direction of shift? Explain with reference to group polarization and the 'risky shift.'
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Reasoning: Group polarization predicts a shift toward the initial majority, not necessarily toward guilt. If the initial majority were not guilty, deliberation should move the group toward acquittal, not conviction. The classic 'risky shift' is a special case: groups sometimes become more risky than individuals, but the direction depends on the initial mean. In this case the initial mean was slightly guilty, so a guilty shift is consistent with polarization. The key comparison is the group's initial position versus its final position, not a universal tendency to be harsher. A 4-2 not-guilty jury would therefore be expected to shift toward not guilty, unless new evidence changed the distribution.