投资者该为耶伦主席送上鲜花美酒了。市场再次因为央行行长的一句话而上涨。在昨天的演讲中，耶伦主席强调了央行和市场的复杂关系，重提了十二月的美联储加息。耶伦主席首次指出：“市场下跌不会引发美联储对经济增长的通货膨胀的担忧，但仍需要提高警惕。面对市场下行，投资者降低了对联邦基金利率的预期，这会给长期利率带来下行风险，缓冲经济活动的负面影响。”
换句话说，市场本身在下跌，美联储就不会采取以前那样严苛的紧缩政策。所以美联储不需要采取额外的行动来稳定经济，美联储的市场参与行动就达到了效果。在加息方面，耶伦补充道：“反思十二月以来的全球经济动态，加息的步伐可能会放缓。举例来讲，联邦公开市场委员会参与者对2016年底联邦基金利率的平均预期为0.9%，2017年底为1.9%，都比十二月低0.5个百分点。”
美联储行动和市场反馈之间的互动早在耶伦上任之前就存在。基金管理公司 GMO 今日发布了一份报告，报告内容是美联储会议当天的市场波动。美联储每年举行八次会议。但自1984年以来，美联储当天会议的反馈只有全部反馈的四分之一。去除这些反馈，美国股票的价格走势便完全符合罗伯特·席勒的周期调整市盈率理论。确实，在危机最严重的时候，市盈率可能会跌至个位数，是美联储阻止了这种情况的发生。
但问题是，研究表明，央行通过量化宽松为资产价格提供的支持变得越来越不平衡，美国、英国皆是如此。但央行认为，为了避免经济崩溃产生更大的威胁，付出这些代价还是值得的。
市场波动时期的干预政策可以追溯到20世纪80年代，那时的价格高得多、稳定得多。现如今利率越来越低，估价越来越高，债务人已经习惯了超低的利率而不断地贷款（这就是政策的重点）。但这也意味着，利率若想回到正常水平，就要付出更高的成本。想一想贷款买房的人突然发现利率变成6-7%会是什么样的情形。如果席勒市盈率从当前的25.6跌至16.7，信心会受到多么大的打击。
央行行长们不愿意让这样的事情发生，而投资者们也了解行长们的想法。所以他们的关系就像一个酒吧招待员和一位酒吧常客，招待员不停地给顾客倒酒，顾客也不停地喝，完全不考虑肝硬化的风险。当然这是个新问题，也许是六年后才会担心的问题。但现在确实没有更好的解决方法了。
Enabling the addiction
TIME for equity investors to send Janet Yellen some champagne, or at least a bunch of flowers. Once again, markets are rising because of something that a central banker said. In a speech yesterday, Ms Yellen highlighted the complex relationship between central banks and markets. Recall that the Fed raised rates in December. Ms Yellen first notes that：
“The proviso that policy will evolve as needed is especially pertinent today in light of global economic and financial developments since December, which at times have included significant changes in oil prices, interest rates, and stock values.”
Those market declines don't mean that the Fed has altered its outlook for economic growth and inflation. But they were still important because, she adds
“investors responded to those developments by marking down their expectations for the future path of the federal funds rate, thereby putting downward pressure on longer-term interest rates and cushioning the adverse effects on economic activity”
In other words, the markets anticipated that, because they themselves were falling, the Fed would not tighten as quickly as before. So the Fed didn't actually need to act to stabilise the economy; market anticipation of Fed action did the trick. As in Keynes's famous beauty contest analogy, we have reached the higher levels of reasoning. Of course, this process still needed the Fed to play along with market reasoning and it is. On the pace of rate rises, Ms Yellen said:
“Reflecting global economic and financial developments since December, however, the pace of rate increases is now expected to be somewhat slower. For example, the median of FOMC participants' projections for the federal funds rate is now only 0.9 percent for the end of 2016 and 1.9 percent for the end of 2017, both 1/2 percentage point below the December medians.”
This relationship between the Fed's actions and market returns dates back well before Ms Yellen's tenure. GMO, a fund management company, recently published a paper looking at market movements on the day of Fed meetings. The Fed only meets eight times a year. But since 1984, the returns on the days of Fed meetings have provided a quarter of all returns. Take those returns away and US equities would look reasonably priced under Robert Shiller's cyclically-adjusted price-earnings ratio methodology. Indeed, in the depths of the crisis, the market would probably have fallen back to a single-digit p/e. The Fed prevented the market from reverting to the mean.
Here is the difficulty. Studies suggest central bank support for asset prices, via quantitative easing, has increased inequality in both America and Britain. But the central banks would argue that this was a price worth paying in staving off the much greater threat of an economic collapse.
But this policy of intervening when markets wobble, dating all the way back to the 1980s, has a steadily higher price. Over time, rates get lower and lower and valuations tend higher. Debtors get used to ultra-low interest rates and keep borrowing (that's the point of the policy, after all). But this means that the potential cost of a reversion to "normal" levels of interest rates gets even greater; imagine what would happen to homeowners if mortgage rates were 6-7%. What would happen to confidence if the Shiller p/e fell from its current 25.6 to the historic average of 16.7?
Central banks don't want that to happen and investors know that central banks don't want it to happen. So the two are locked together like a barman and his most profitable customer, endlessly pouring one more drink to fend off the hangover and trying to forget about the cirrhosis that might set in. This is not a new problem, of course; your blogger was worrying about it six years ago. But we don't seem to be any nearer solving it.
本文翻译由兄弟财经提供
文章来源：http://www.economist.com/blogs/buttonwood/2016/03/central-banks-and-markets