For multiple reasons, deliberating groups often converge on falsehood rather than truth. Individual errors may be amplified rather than cured. Group members may fall victim to a bad cascade, either informational or reputational. Deliberators may emphasize shared information at the expense of uniquely held information. Finally, group polarization may lead even rational people to unjustified extremism. By contrast, prediction markets often produce accurate results, because they create strong incentives for revelation of privately held knowledge and succeed in aggregating widely dispersed (...) information. The success of prediction markets offers a set of lessons for increasing the likelihood that groups can obtain the information that their members have. (shrink)

Reasoning may be defined as a deliberate effort to coordinate inferences so as to reach justifiable conclusions. Thus defined, reasoning includes collaborative as well as individual forms of cognitive action. The purpose of the present study was to demonstrate a circumstance in which collaborative reasoning is qualitatively superior to individual reasoning. The selection task, a well known logical hypothesis-testing problem, was presented to 143 college undergraduates-32 individuals and 20 groups of 5 or 6 interacting peers. The correct (falsification) response pattern (...) was selected by only 9% of the individuals but by 75% of the groups. The superior performance of the groups was due to collaborative reasoning rather than to imitation or peer pressure. Groups typically co-constructed a structure of arguments qualitatively more sophisticated than that generated by most individuals. The results support Piagetian and Habermasian views of peer interaction as a locus of rational social processes. (shrink)

The contemporary theory of epistemic democracy often draws on the Condorcet Jury Theorem to formally justify the ‘wisdom of crowds’. But this theorem is inapplicable in its current form, since one of its premises – voter independence – is notoriously violated. This premise carries responsibility for the theorem's misleading conclusion that ‘large crowds are infallible’. We prove a more useful jury theorem: under defensible premises, ‘large crowds are fallible but better than small groups’. This theorem rehabilitates the importance of deliberation (...) and education, which appear inessential in the classical jury framework. Our theorem is related to Ladha's (1993) seminal jury theorem for interchangeable (‘indistinguishable’) voters based on de Finetti's Theorem. We also prove a more general and simpler such jury theorem. (shrink)

Suppose a committee or a jury confronts a complex question, the answer to which requires attending to several sub-questions. Two different voting procedures can be used. On one, the committee members vote on each sub-question and the voting results are used as premises for the committee’s conclusion on the main issue. This premise-based procedure can be contrasted with the conclusion-based approach, which requires the members to directly vote on the conclusion, with the vote of each member being guided by her (...) views on the relevant sub-questions. The two procedures are not equivalent: There may be a majority of voters supporting each of the premises, but if these majorities do not significantly overlap, there will be a majority against the conclusion. Pettit (2001) connects the choice between the two procedures with the discussion of deliberative democracy. The problem we want to examine instead concerns the relative advantages and disadvantages of the two procedures from the epistemic point of view. Which of them is better when it comes to tracking truth? As it turns out, the answer is not univocal. On the basis of Condorcet’s jury theorem, the premise-based procedure can be shown to be superior if the objective is reach truth for the right reasons, without making any mistakes on the way. However, if the goal instead is to reach truth for whatever reasons, right or wrong, there will be cases in which using the conclusion-based procedure turns out to be more reliable, even though, for the most part, the premise-based procedure will retain its superiority. (shrink)

James Madison wrote, 'Had every Athenian citizen been a Socrates, every Athenian assembly would still have been a mob'. The contributors to this volume discuss and for the most part challenge this claim by considering conditions under which many minds can be wiser than one. With backgrounds in economics, cognitive science, political science, law and history, the authors consider information markets, the internet, jury debates, democratic deliberation and the use of diversity as mechanisms for improving collective decisions. At the same (...) time, they consider voter irrationality and paradoxes of aggregation as possibly undermining the wisdom of groups. Implicitly or explicitly, the volume also offers guidance and warnings to institutional designers. (shrink)