20190225【充实计划】第991期

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昨天继续学习了经济学中福利经济学中的行为经济学的思维，以色列心理学家丹尼尔·卡尼曼（D a n i e l  K a h n e m a n）研究视觉感知的心理学，随后又转向经济学。他的一个研究心理学的同事阿莫斯·特沃斯基（Amos Tversky）发现当人们接受一份工作或者购买一杯咖啡时，一道心理的浓雾会令他们没有办法有逻辑地理解事情。经济学家一直相信人是理性的，人们会在展开行动前精确地权衡选择的成本和收益。卡尼曼和特沃斯基发现事实并非如此。他们用了几十年观察人类在事实生活中的决策，并帮助创建了行为经济学。人以不同的方式权衡收获和损失，理性来讲，收获50美元正好可以抵消损失50美元。但是比起收获，人们看起来都更讨厌损失。一间屋子看起来是更亮还是更暗，要看屋外的亮度一样，结果看起来是更好还是更糟要看你的基准点（reference point）在哪里。通过对某件事物在和基准点的对比中进行描述或“框定”（framed），人们的决定可以仅因此受到影响。基准点让人们无法单纯以金钱的得失为基础理性地做出决策。如果一台笔记本计算机以1000美元的价格进行促销，看起来也不过如此；同一台电脑如果是从1500美元打折到1000美元，看起来就显得很便宜。超市利用这一点，将一些商品的价格先提高，然后再大力打折。决策中另一个无逻辑的事情是人们对不确定性的判断，如果人是理性的，那么他们应该能够很好地利用他们所能获得的信息，并以此为基础评估未来的可能性。卡尼曼和特沃斯基认为，人不是这样的。些经济学家承认人类决策的无逻辑性，但还是认为这并不重要，将经济大致描述为理性的是有益的。另一方面，行为经济学家却解释主要的经济活动需要他们独特的理论。比如，行为经济学已经被用来解释20世纪90年代美国股票市场的飙升以及2000年的暴跌、企业破产和财富的消失。罗伯特·希勒（Robert Shiller）将行为经济学应用到金融市场上。他说，金融市场因为乐观情绪被推高，但很快就会回落。人们决策当中的无逻辑性是股市失去控制的原因。希勒认为，20世纪90年代的股票市场，更像是时尚，而并非理性的经济学。人们模仿别人的穿著，某年流行大镜面的太阳镜，越多人戴这样的太阳镜，就有越多人想要加入进来。一个失控的股票市场是以股价进行表达的一场经济学时尚。经济学家有时候将市场描述为羊群——成千上万的人跟随前面的人——或者一个风中的肥皂泡，随着股价的上涨而上升。当泡沫破裂时，人们开始朝相反的方向奔跑。人们看到其他人在出售股票，于是也开始出售，很快市场就出现了恐慌。

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The financial crisis of 2007-2009 taught us many lessons about monetary policy. Most importantly, we learned that when financial systems are impaired, central banks can backstop both illiquid institutions and illiquid markets. Actively lending to solvent intermediaries against a broad range of collateral, purchasing assets other than those issued by sovereigns, and expanding their balance sheets can limit disruptions to the real economy while preserving price stability. We also learned that nominal interest rates can be negative, at least somewhat.

But in reducing interest rates below zero―as has happened in Denmark, Hungary, Japan, Sweden, Switzerland and the Euro Area―policymakers face concerns about whether their actions will have the desired expansionary effect. At positive interest rates, when central bankers ease, they influence the real economy in part by expanding banks’ willingness and ability to lend. Does this bank lending channel work as well when interest rates are negative?

In normal times, interest rate reductions have two complementary effects that promote lending. First, banks’ net worth rises because their assets are longer maturity than their liabilities. Second, by driving up asset values and improving business prospects, accommodative policy improves the creditworthiness of potential borrowers. This increase in both the supply and the demand for loans boosts lending and spurs real activity.

Why should there be any sort of asymmetry at zero? Banks run a spread business: they care about the difference between the interest rate they charge on their loans and the one they pay on their deposits, not the level of rates per se.

In practice, however, zero matters because banks are loathe to lower their deposit rates below zero. Their reluctance is apparent from the following chart, which shows the configuration of various interest rates for the euro area starting in 2000. Prior to 2008, these data exhibit what we would label as the textbook case. The interest rate banks pay their corporate depositors is slightly higher than what they pay households. But both of these are below the rate that the bank can obtain by depositing funds overnight at the central bank, which is less than what banks get for lending to other banks overnight. Then comes the crisis and the spread between the deposit rates and the overnight interbank lending rate disappears. And, when the ECB implements its negative interest rate policy in 2014, lowering the rate banks receive for deposits at the central bank below zero, the spread becomes negative. From an individual bank’s perspective, what used to be a profitable business of taking corporate or household customer deposits and either simply placing the proceeds at the central bank or lending it to another bank, now results in a loss.
Looking at this, one might think that a shift to negative rates would drive the whole transmission mechanism into reverse. That is, rather than promoting bank lending―which requires that banks attract funds―pushing the policy interest rate below zero would cause intermediaries to shrink their balance sheets in order to reduce their losses. The more negative the policy rate, the more contractionary the policy.

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