Imperfect common knowledgeと中央銀行の透明性、最適な金融政策

　昨日頂いたさとるさんのコメントから、あまりこの種のテーマはいまいち気乗りしなかったんだけども、それでも以下のペーパーは最新だし、いまの日本の状況（noisy public signal、deflationary bias etc）を考えたときに重要かもしれないのでメモとして。講義開始と原稿締め切りでちょっと多忙。他にもいろいろあるのでリンク集のEconpapersにImperfect common knowledgeを入力してみてください。Baeriswylの論文や、あとスベンソン、ウッドフォードの論文が参考になる。

１　Monetary Policy and its Informative Value（Camille Cornand and Romain Baeriswyl ）
http://www.frbsf.org/economics/conferences/0703/cornand_baeriswyl.pdf

Abstract: This paper analyzes the welfare effects of economic transparency in the conduct of monetary policy. We propose a model of monopolistic competition with imperfect common knowledge on the shocks affecting the economy where the central bank has no inflationary bias. In this context, monetary policy entails a dual role. The instrument of the central bank is both an action that stabilizes the economy and a public signal that partially reveals to firms the central bank's assessment about the state of the economy. Yet, firms are unable toperfectly disentangle the central bank's signals responsible for the instrument and the central bank optimally balances the action and information purposes of its instrument. We derive the optimal monetary policy and the optimal central bank's disclosure. We define transparency as an announcement by the central bank that allows firms to identify the rationale behind the instrument. It turnsout that transparency is welfare increasing (i) when the degree of strategic complementarities is low, (ii) when the economy is not too affected by mark-up shocks, (iii) when the central bank is more inclined towards price stabilization, (iv) when firms have relatively precise private information, and (v) when the central bank's information is relatively precise on demand shocks and relatively imprecise on mark-up shocks. These results rationalize the increase in trans-parency in the current context of relative low sensitivity of the economy to mark-up shocks and of strong central bank's preference for price stability.JEL classification: E52, E58, D82.Keywords: differential information, monetary policy, transparency.

２　Central Bank's Action and Communication（Romain Baeriswyl）
http://epub.ub.uni-muenchen.de/1381/1/Baeriswyl_CBAC.pdf

Abstract: This paper contributes to the ongoing debate about the welfare effect of public information. In an environment characterized by imperfect common knowledge and strategic complementarities, Morris and Shin (2002)argue that noisy public information may be detrimental to welfare because public information is attributed too large a weight relative to its face value since it serves as a focal point. While this argument has received a great deal of attention in central banks and in the financial press, it considers communication as the sole task of a central bank and ignores that communication usually goes with a policy action. This paper accounts for the action task of a central bank and analyzes whether public disclosure is beneficial in the conduct of monetary policy when the central bank primarily tries to stabilize the economy with an instrument that is optimal with respect to its perhaps mistaken view. In this context, it turns out that transparency is particularly beneficial when central bank’s information is poorly accurate because it helps reducing the distortion associated with badly suited policies.

　それと以下の論文集のウッドフォード論文、経済学史好き？にはフェルプスのコメントがケインズ、ナイト、ハイエクとの関連を示していて有益。特に「ナイトの不確実性」をフェルプスは彼の言葉でいうところの不完全知識の問題で読み替えているところは、今日でも竹森俊平さんの以下であげた本の主張を理解するうえで興味深いだろう。

Knowledge, Information, and Expectations in Modern Macroeconomics: In Honor of Edmund S. Phelps

1997年――世界を変えた金融危機 (朝日新書 74)

こんなことしている暇はないな。焦る。

（付記）書き忘れたが、わが中銀は、例のリーク問題で象徴されたり、事後的にこれはまずいと自己規制した前総裁のようなインサイダー疑惑体質など、正直いって上のようなテクニカルな論文を読まなくても、常識＝世間知で十分批判できる。もし上記の英文及び英語論文の中味が困難に感じられる方は、手前味噌で濃すぎるが、拙著『不謹慎な経済学』のリーク関連を読まれれば、事実上Romain Baeriswyl論文で主張されていることと同じものを読むことができるだろう。