Secret ballots and costly information gathering: The jury size problem revisited

Suppose paying attention during jury trials is costly, but that jurors do not pool information (as in contemporary Brazil, or ancient Athens). If inattentive jurors are as likely to be wrong as right, I find that small jury panels work better as long as identical jurors behave symmetrically. If not paying attention makes error more likely than not, jurors may coordinate on two different symmetric outcomes: a “high attention” one or a “low attention” one. If social norms stigmatize shirking, jurors coordinate on the high attention equilibrium, and a smaller jury yields better outcomes. However, increasing the jury up to a finite bound works better if norms are tolerant of shirking, in which case coordination on the low attention outcome results. If jurors always act as if they are pivotal, a larger jury may work better. Allowing deliberations is efficient if the jury panel is relatively large, and if the police and prosecution are effective. However, barring deliberations is better at smaller jury sizes, specially if the police and prosecution are not too efficient.