注册 登录  
 加关注
   显示下一条  |  关闭
温馨提示!由于新浪微博认证机制调整,您的新浪微博帐号绑定已过期,请重新绑定!立即重新绑定新浪微博》  |  关闭

TheMoneyIllusion货币幻觉

美国本特利大学经济学教授斯科特·萨姆纳(Scott Sumner)

 
 
 

日志

 
 
关于我
Sumner  

美国本特利大学经济学教授

文章分类
网易考拉推荐

为“指手划脚”正名  

2009-05-29 11:29:05|  分类: 默认分类 |  标签: |举报 |字号 订阅

  下载LOFTER 我的照片书  |

  [点击查看Scott Sumner的英文博客]

 为了更好地解释我早些时候关于因果关系和名义GDP目标制(NGDP targeting)的评论,这里我试着打几个比方。不过你很快也会看到,我的文学水平并不怎么样。

船长Ben驾驶一艘大型远洋游轮出海,途中必须从两个沙地岬角间驶过。可是一股稳定的风却将船推向左侧的沙洲。这时船长有足够的时间调整方向舵轮和发动机控制以抵消风力,但船长没有及时采取行动,船继续向左漂移,最终陷入了沙洲。是船长的疏忽导致了事故吗,还是因为风?

故事说到这里,似乎还没有说到点子上。现在我再添加一些新的细节,借以阐释我之前发过的文章。

假设控制室里还有十几个经验丰富的船长,外加一个学员。没有任何一名船长认为Ben在这件事上有失职嫌疑;大部分都说,他已经尽了全力,甚至其中还有一些表示他做得太卖力,他们认为:“我们真的不知道这风会刮多久,往哪刮。”只有那名学员认为船长做得不够,而且随着船不断向左侧的沙洲移动,他变得越来越不安。他的建议也越来越急躁:

“把舵轮进一步向右转,你还没有把它转到底。”

“快打开辅助快速点火喷射器(帮助在近距离时操控船舶的侧装水流喷射器)。”

 “你没看到我们正直奔沙洲而去吗!”

船长终于把舵轮向右转到底,但学员仍喋喋不休地坚持着要打开快速点火喷射器(QE):“如果你等我们撞上沙洲才打开,到时候QE还有什么用呢!”

“你必须现在立刻采取行动!”

其他船长无情地嘲笑着那名学员: “没错,‘让她全速前进吧,Scotty!’(星际迷航中的台词,借以讽刺该学员)”

一些船长窃窃私语,怀疑他曾经上的是一所淡水训练学校,那里的学生只学会了湖上泛舟的本领。

 “这个可怜的傻瓜根本不了解海上驾船的技巧。 ”

“是啊,他肯定是中西部来的。”

最终船陷在了沙洲里,乘客们被告知船舶可能需要等几个月才能被拖离。大家都很担心如此长期的离岗之后各自的工作情况会如何。

而这个时候QE终于被开启,但是因为大部分船体仍然陷在沙里,船反应得非常缓慢。

“哈,正如我所想,QE也帮不上忙,我就知道那个学员都是在胡说八道。”

 

好吧,这个故事又臭又长,但因果关系的问题到底是怎样呢,是船长造成事故的吗?在我之前的言论中我提到,如果其他大多数专业人士也做了相同的决策,那么就很难判定责任归属。因此,Ben船长不能因事故而遭“指责”。另一方面,如果有一个备选的驾驶“策略” ,而该策略可以阻止事故发生,船长也有足够的时间作出反应,那么可以说事故的原因是没有正视这种“船长驾驶制度”。我认为没有人会愚蠢地辩驳说,只有在船长把舵轮转向错误方向的情况下,才能说是船长造成了意外。若直行河道中有明显的弯折,而这个时候船长还稳定向前地驾驶,那么他也需要对事故负责。

那么,我们今后要如何防范此类事故呢?答案在于鼓励那些“后座司机”(坐在汽车后座对司机指手画脚的人)。 是的,我知道我的绝大多数男性读者都驾驶技术出众。而我也敢肯定你们不喜欢那些坐在后座指手画脚的人。但偶尔这样真的有什么不好吗?

我并不打算再次详细阐述名义GDP(NGDP)目标制计划,这一点我们已经探讨过了。但我注意到,许多评论者都担心如果没人进入这一政策市场会发生什么情况。我的回答是,没什么坏事会发生。每一天开始时,美联储都该将基数设定在一个预计能产生目标增长(例如5 % NGDP增长)的水平。如果没有人进入市场,那么我们可以推测,交易商认为美联储干得不错。那样就很好。

另一方面,我认为去年9月和10月很明显的是, NGDP增长要远远低于现在的目标。我也许要等待数天去观察市场是否有猛增,但如果没有,我会抓住方向盘,尽我全力——或者应该说我全部的钱——将之扭转向正确的方向。我们都抱怨过美联储的政策,如果我们能按照自己的意愿进行投资,岂不很好?为什么要让某一个船长(或者甚至12个)独享了这份乐趣呢?

的确,我知道99.9 %的时间里坐在后座指手划脚的人都很讨厌。但总有一个时候,他们会指出你没有看到的孩子、狗或者红灯。在这种情况下,他们说些什么难道不比让他们闭嘴更好吗?

(翻译纠错:读者发现任何翻译错误,请发邮件给我们,谢谢。caijingblog#126.com;将#改为@ )


英文原文(地址:http://blogsandwikis.bentley.edu/themoneyillusion/?p=1385):

In praise of backseat drivers

Here I’ll try a couple analogies to better explain earlier posts on causation and NGDP targeting.  As you will soon see, my literary skills are at the 5th grade level.

Captain Ben is piloting a large ocean-going cruise ship toward the open ocean, but must steer between two sandy headlands.  A steady wind is pushing the ship to the left, toward one of the sand-bars.  The captain has plenty of time to adjust the rudder and engine controls to counteract the wind, but reacts too slowly and the ship continues to drift to the left, eventually getting stuck on the sandbar.  Did the captain cause the accident through negligence, or did the wind cause the accident?

Not much of an analogy so far, but let’s add a few new elements to correspond to my earlier causation post.

Now assume the control room is full of a couple dozen other experienced ship captains who are on the cruise, and one trainee.  None of the ship captains suggest Ben is doing too little to offset the wind; most say he is doing all he can and a few even suggest he is doing too much, arguing “we don’t really know whether this wind will persist.”  Only the trainee thinks the Captain is doing too little, and he becomes increasingly agitated as the ship seems to be drifting to the sandbar on the left.  His suggestions grow more and more frantic:

“Turn the wheel further to the right; you haven’t turned it as far as it will go.”

“Turn on the auxiliary quickfiring ejectors (side mounted water jets that help steer the ship in close quarters.)”

“Don’t you see we’re headed right for the sandbar!”

Eventually the captain did turn the wheel all the way to the right, but the trainee kept on babbling on about the quickfiring ejectors:

“If you wait till we hit the sandbar the QEs won’t be nearly as effective!”

“You must act now!”

The other ship captains mocked the trainee mercilessly:

“That’s right, give her all she’s got, Scotty”

Some whispered that he had gone to one of those fresh water training schools, where they learned how to steer “boats” on the Great Lakes.

“That poor fool just doesn’t understand what’s involved in steering the big ships in salt water.”

“Yeah, he’s originally from the Midwest.”

Eventually the ship did get stuck on the sandbar.  The passengers were told it might be months before the ship could be dislodged.  There was great concern about what would happen to their jobs after such a long period of unemployment.

Now the QEs were finally turned on, but the ship responded very slowly, as most of the hull was still stuck on the sandbar.

“Ha, just as I thought, those QEs are not very effective; I knew that trainee was babbling nonsense.”

OK, the story is both silly and self-indulgent, but what about the question of causality, did the captain cause the accident?  In my earlier post (here) I argued that it was hard to assign moral culpability if most other experts would have done the same.  So Captain Ben cannot be “blamed” for the accident.  On the other hand if there is an alternative steering “policy” that would have prevented the accident, and if the captain had plenty of time to react, then one could say the accident was caused by not setting the steering mechanism at the right position.  I don’t think anyone would be so foolish as to argue the captain could only be said to have caused an accident if he turned the steering the wrong way.  Even a policy of holding the steering wheel steady could be said to cause an accident when there is an obvious bend in the river straight ahead.

So how do we prevent these accidents in the future?  The answer is to encourage “back seat drivers.”  Yes, I understand that my overwhelmingly male readership is almost all composed of above average drivers, make that well above average.  And I’m pretty sure most of you don’t like back seat drivers.  But is there really anything wrong with an occasional nudge?

I’m not going to spell out the NGDP targeting plan again, it’s discussed here.  But I did notice that many commenters were concerned about what would happen if nobody entered this policy market.  My response is that nothing bad would happen.  At the beginning of each day the Fed should set the base at a level expected to produce on target growth (say 5% NGDP growth.)  If no one enters the market, then we can presume that traders think the Fed is doing a pretty good job.  And that would be fine.

On the other hand last September and October it was obvious to me that NGDP growth was going to come in well below target.  I might have waited a few days to see if the market jumped in, but if they didn’t I would have grabbed the wheel and yanked it to the right with all my strength, or should I say all my dollars.  We’ve all complained about Fed policy, wouldn’t it be nice to be able to put our money where our mouth is.  Why should just one captain, or even twelve, have all the fun.

Yes, I know that 99.9% of the time backseat drivers are annoying.  But there is always that one time when they point out the child, or dog, or red light you didn’t see.  In that case isn’t it better that they say something, rather than keep their mouth shut?

 

 

  评论这张
 
阅读(1581)| 评论(12)
推荐 转载

历史上的今天

评论

<#--最新日志,群博日志--> <#--推荐日志--> <#--引用记录--> <#--博主推荐--> <#--随机阅读--> <#--首页推荐--> <#--历史上的今天--> <#--被推荐日志--> <#--上一篇,下一篇--> <#-- 热度 --> <#-- 网易新闻广告 --> <#--右边模块结构--> <#--评论模块结构--> <#--引用模块结构--> <#--博主发起的投票-->
 
 
 
 
 
 
 
 
 
 
 
 
 
 

页脚

网易公司版权所有 ©1997-2017