金融危機過後，利率仍保持為零，央行試圖用各種新舉措來刺激經濟。政策之一是前瞻指引：承諾將貨幣寬松政策維持一段時間。美聯儲在2011年表示，低利率將持續至2013年中，隨後又延續到2014年，接著推遲到2015年。前瞻指引現已成為貨幣政策的工具之一。一旦利率上升，如果使用這個工具才能達到最佳效果呢？上週，紐約芝加哥佈斯的貨幣政策論壇發佈了一篇文章，認為在正常情況下，央行的承諾不一定有用。
前瞻指引有兩種，其一為時間表。美聯儲剛剛在十月採用了這一方式，他們在會後聲明中強調了下一次會議的重要性，而美聯儲確實在十二月的會議中宣佈加息。另一種方式是不公佈具體時間，只說明總體方針，指明形勢向不同方向轉變時利率將如何變化。舉例來講，英格蘭銀行在2014年承諾，在失業率降至7%之前，不會加息。Michael Feroli、David Greenlaw、Peter Hooper、Frederic Mishkin以及Amir Sufi認為，由數據驅動的指引要強於時間表。數據驅動的指引能夠清晰地表明央行的態度和傾向，它的好處有兩點。首先，如果市場事先了解美聯儲修改利率的計劃，那麼利率變化之時，投資者們就不會亂發脾氣了。在美聯儲十二月加息之時，加息的消息早已衆所週知，這意味著市場不會出現大幅波動。其次，如果利率緊隨金融態勢發生變化，貨幣政策就具備了自動轉向的能力，在美聯儲採取措施之前，貨幣政策已經對事件做好了反應。
既然提到了政策時間表，就不得不提及成本問題。首先，時間表會同數據驅動的指引發生沖突。財經媒體和交易員在關註匯率變化時間表的同時，會忽略與之相伴的預警。更嚴重的情況，時間表式的指引會與數據驅動的指引大相徑庭，會讓市場誤以為美聯儲的政策只會按計劃進行，而忽略了實際的經濟形勢。這樣的貨幣政策是事先制定好的，不能像數據驅動的指引一樣進行自我修正。事實證明，美聯儲越強調加息時間，投資者們越容易忽略財經消息。
但在利率維持在較低水平時，時間表還是比較有時效性的。刺激經濟增長並擺脫流動性陷阱的一種方法就是承諾未來的通脹率會增加。央行做出如此承諾卻很難讓人信服，因為他們一旦逃離了流動性陷阱，立刻會對激增的通脹進行打壓。除非他們敢承諾在經濟複蘇之後仍保持寬松的貨幣政策。在會議中，舊金山聯儲主席和前任利率設定者一致認為，在危機後的通信中，美聯儲該做的是指出一條明確的出路，而不是讨論哪條路更好。
正常時期的通信也很讓人擔心。評論員過分關註於時間表，就連英格蘭銀行7%的失業率閥值都被市場和媒體忽視了。這意味著時間表是無可避免的。除此之外，時間表簡單易懂，不同形勢下採取的不同措施卻很難解釋，尤其是在官員們都各持意見難以說清的時候。就算看在時間表簡單易懂的份上，央行也不能將之隨意抛棄。
Should central banks offer timelines for monetary policy?
After the financial crisis, with interest rates stuck at zero, central banks tried to gee up economies with a variety of new measures. One was forward guidance: pledging to keep policy loose for a while. In 2011 the Federal Reserve said it expected rates to remain low until mid-2013; this was then pushed back to mid-2014, then mid-2015. Forward guidance is now an established part of the monetary policy toolkit. But what is the best way to deploy it once interest rates are rising? A new paper, presented last week at Chicago Booth’s Monetary Policy Forum in New York, argues that in normal times, not all central bank promises are equal.
There are two types of forward guidance. One uses a timeframe. The Fed did this most recently in October when, in its post-meeting statement, it referred explicitly to the importance of the next meeting (in December, when it raised rates). The alternative is not to mention dates, but say how, in general, interest rates would respond to different turns of events. For example, in 2014 the Bank of England promised—with some caveats—not to raise rates until unemployment fell below 7%.
Michael Feroli, David Greenlaw, Peter Hooper, Frederic Mishkin and Amir Sufi argue that in normal times, data-dependent guidance beats a schedule. Data-based guidance helps mainly by demystifying the central bank’s preferences. That is beneficial for two reasons. First, if markets know how the Fed will change rates when the economy soars or sours, they will not throw a tantrum when rates change. When the Fed raised rates in December, its move was widely expected. That meant markets barely moved. Second, if market interest rates respond immediately to economic news, monetary policy benefits from automatic steering; financial conditions automatically loosen and tighten in response to events, before the Fed actually turns the steering wheel.
But mentioning timelines for policy, the authors argue, comes with costs. First, timelines distract from data-driven guidance. The financial press and traders focus on any hint of a schedule for changes in interest rates, and often ignoring the accompanying caveat. Worse, time-based guidance can work against data-based guidance, by leading markets to think that the Fed will stubbornly stick to its plan whatever happens to the economy. Monetary policy is set on cruise control but, unlike with data-driven guidance, it does not steer itself. The authors present evidence that market interest rates become less sensitive to economic news the more the Fed mentions timelines or dates in its statements.
Timelines may remain sensible, though, when interest rates are at their lower bound. One way to stimulate the economy and escape a liquidity trap is to promise higher inflation in the future. It is tough for central banks to make such promises credibly; having escaped the liquidity trap, their instinct will be to clamp down on resulting inflation. It might therefore be helpful if they can tie their own hands, promising to keep policy loose even after the recovery. At the conference both John Williams, president of the San Francisco Fed, and Jeremy Stein, a former rate-setter, suggested that post-crisis Fed communications were partly an attempt to commit to a given path, rather than merely to communicate preferences.
The authors, though, are concerned with communication in more normal times. And they have a point about commentators’ obsession with timelines; even the Bank of England’s 7% unemployment threshold was immediately interpreted by markets and the press as providing a timeline for a rate rise, when paired with the Bank’s unemployment forecast. That suggests, though, that it is tough to avoid timelines altogether. And schedules come with the virtue of simplicity; guarded statements about possible different paths for rates can be tricky to interpret, especially when they are the work of a committee whose members’ individual views differ. Central banks should not throw out the planner entirely—if only for simplicity’s sake.
本文翻譯由兄弟財經提供
文章來源：http://www.economist.com/blogs/freeexchange/2016/03/dates-vs-data