Public Information and Information Aggregation in Committees

公開訊息對投票行為影響之探討

吳震台(Cheng-Tai Wu)

《經濟論文叢刊》 47卷3期 (2019/09) Pp. 321-361

https://doi.org/10.6277/TER.201909_47(3).0001

摘要

We investigate how public information affects the voting behavior of the voters and the error (information efficiency) of the equilibrium decision of a committee. The influence of public information on efficiency can be decomposed into the information effect and the equilibrium effect. Public information provides an extra piece of information that helps the voters better match their votes with the received signals, and hence may reduce the error. However, it also affects the equilibrium behavior of the strategic voters, and this may increase the error. We show that for any non-unanimous voting rule, when the precision of public information is marginally higher than that of private information, the information effect is negligible, while the equilibrium effect has negative impact on efficiency. Hence, public information with low precision may make the decision of the committee worse. By contrast, for the unanimous rule, the equilibrium effect has positive impact and public information will always improve the efficiency. Furthermore, we find that the existence of non-strategic voters may cause asymptotic inefficiency when the voting rule is too stringent in the sense that it is far away from the simple majority rule. Public information can de facto alter the voting rule to be less stringent through its influence on the votes of the non-strategic voters. Thus, the efficiency can be improved.

關鍵字

strategic voting ； public information ； Condorcet jury theorem

並列摘要

本文探討公開訊息（public information）如何影響投票行爲及結果。其影響可以分解成訊息效果（the information effect）和均衡效果（the equilibrium effect）。公開訊息一方面提供額外的訊息，讓投票者做出較好的決。另一方面，由於策略性的投票，公開訊息會影響投票者的均衡行爲。我們發現，對任何非全體決的投票規則（non-unanimous voting rules），當公開訊息的準確度（the precision of public information）低時，訊息效果可以忽略，但是均衡效果會產生負面的影響，因此，公開訊息反而會讓投票結果的錯誤增加。相反的，在全體決下（the unanimous voting rule），均衡效果的影響是正面的，因此，公開訊息會改善投票的結果。我們進一步探討非策略性投票者（non-strategic voters）對投票結果的影響，當存在這些投票者時，公開訊息實質上（de facto）改變了現存的投票規則，如果這個改變讓實質的規則更接近最適的投票規則，公開訊息就會改善投票的結果。

並列關鍵字

策略性的投票 ； 公開訊息 ； Condorcet jury theorem

參考文獻

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