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 co-ordinate on two different symmetric outcomes: a “high-attention” one or a “low attention” one. If social norms stigmatize shirking, jurors co-ordinate 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 co-ordination on the low-attention outcome results. If the cost of attention is high, a bare majority of jurors pay attention, and efficiency increases in jury size up to a bound. The model also applies to elections and referendums