Fabrizi, S., Lippert, S., Pan, A., Ryan, M., 2022. A theory of jury voting with an ambiguous likelihood. Theory and Decision 93, 399–425 (supported by Marsden Grant UOA1617).
We examine collective decision-making in a jury voting game under the unanimity rule when voters have ambiguous beliefs. Unlike in existing studies (Ellis, 2016; Fabrizi, Lippert, Pan, and Ryan, 2020; Ryan, 2021), the locus of ambiguity is the likelihood function (signal precision) rather than the prior. This significantly alters the properties of symmetric equilibria. While prior ambiguity may induce multiple equilibria (Fabrizi et al., 2020; Ryan, 2021) we show that all (non-trivial symmetric) equilibria under likelihood ambiguity have the same form as in the absence of ambiguity (Feddersen and Pesendorfer, 1998). Moreover, likelihood ambiguity partially offsets the pernicious effects of pivotality on decision quality: there exists an equilibrium in which the frequency of Type I error (convicting the innocent) is typically lower than in the absence of ambiguity. This, too, is in contrast to prior ambiguity, which has the opposite tendency (Ellis, 2016; Fabrizi et al., 2020; Ryan, 2021).