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楼主: 我心依旧

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一场难忘的讨论（五） [推广有奖]

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我心依旧 发表于 2004-10-4 15:41:00 |只看作者 |坛友微信交流群|倒序 |AI写论文

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Re:我所知道的张五常（李俊慧）（之五）--道德风险作者:dzz　　发表时间:2001年5月19日 08:51 说用“道德风险(Moral Hazard)”来解释买保险后车祸的比例会上升是套套逻辑(tautology)不错，但以次来批判道德风险的研究是投梁换柱。树立一个并不存在的靶子，以之来代替真正的目标，把它打倒,然后宣称胜利，这就是上文对道德风险研究的批判。道德风险研究的主要是如何避免道德风险和合约的设计，而不是解释买保险后车祸上升的现象。 Re:我所知道的张五常（李俊慧）（之五）--道德风险作者:lijunhui　　发表时间:2001年5月19日 09:14 不好意思，套套逻辑的英文我写错了。因为是在学校的机房上网，不能参考原文来写，凭记忆难免有错。还有打字太快了，有些地方也出了错，请原谅。上面的朋友说：“道德风险研究的主要是如何避免道德风险和合约的设计，而不是解释买保险后车祸上升的现象。”实际上已经同意了我的意思。要注意经济学的方法论，科学（包括经济学）理论是为了解释现象，而不是解决问题。既然道德风险的研究没有解释买保险后车祸上升的现象，那就不是理论。解释现象和解决问题的不同，我后面会说，这里只简单将要点说一下。解决问题只需要把握规律，不需要构建理论；而解释现象是要构建规律以外的抽象理论。所以，把解决问题当成解释现象是犯了“事实不能解释事实”的错误。 Re:我所知道的张五常（李俊慧）（之五）--道德风险作者:dzz　　发表时间:2001年5月19日 09:20 经济学的范畴有过很多讨论，大部分认为包括实证和规范两部分，看一看张五常最崇拜的Friedman的论述就知道。 Re:我所知道的张五常（李俊慧）（之五）--道德风险作者:Ah sa　　发表时间:2001年5月19日 12:16 "人们买了保险，的确是会放松警惕，车祸的比例会上升。但为什么会出现这种情况？你不能说是因为“道德风险”，因为“道德风险”的定义就是买了保险故意撞车，用定义去解释定义，不是同义反复是什么？" (1) My interpretation of (李俊慧's interpretation of) Cheung's arguement is that: - Moral hazard assumes people cheats when monitoring is imperfect. So if we use moral hazard to explain why people "cheats". It would be tautological. (2) Firstly, I don't think "“道德风险”的定义就是买了保险故意撞车", moral hozard just constructs a situation with the type of asymmetries of information that develop subsequent to the signing of a contract. "买了保险故意撞车" is the result of the maximization postulate in this moral hazard setting. So you can say this is an immediate dedeuction result, but not a tautology. (Note, however, results of logical dedeuction is by definition always consistent with the assumptions. So if you want, you can consider all assumptions, relevant definitions and deduced implication as a proposition as a whole, in this case, it is always a tautology!) (3) Yes, you're right. It is meaningless to answer why people cheats by assuming it. But as far as I know, moral hazard models are not aimed to answer this question. ( Just like (traditional) monetary economics is not aimed to answer the question why we have money, but just assume its existence. If you use monetary theory to answer this question, it would be tautological.) Instead, they consider, given a moral hazard setting, how can we explain certain behaviour of agents or contractual arrangements. For example, in the case of insurance, we consider how the equilibrium insurance contract depends on the information structure (observibility of agents'action) and other exogenuous variables. We want to know when we will have a full/partial compensation contract. Is an answer to this type of question a tautology? Another example is the moral hazard game of firm owners & managers. We DO NOT use moral hazard to explain why agents shirk. But we assume imperfect monitoring, and see how equilibrium wage contracts are determined. For example, we want to see in what situation we will have a fixed wage contract, a proportional contract, a linear contract, a short-term contract, a long-term contract, a tournamant (eg. promotion reward). How the equilibrium contractual arrangement are related to the information structure, monitoring cost, number and characteristics of agents, ... Are answers to these questions tautological? Are all these implications not testable? I don't think so. (4) You may say "hey, we can explain all these very well by using the concept of transaction cost." In principal, yes. I guess you can re-label the information variable & monitoring cost by the concept of transaction cost. But is that really a better and clearer approach? To be a reasonable candidate, at least we need to know what transaction cost exactly mean. Because if we don't specify what tranaction cost refers to in real life, we can always use transaction cost as a "residual term". Whatever we see, we can say, "oh, because the transaction cost is so high/low that we observe this phenomena ..." If this is the case, the explanation using transaction cost becomes not refutable! That's why I always ask for a precise definition of this concept. According to Cheung's definition, it seems that the cost of "playing tennis" is also a transaction cost. This is because playing tennis is not conceivable in an one man economy. That's surely not a good definition, no? 学无新旧，学无中西，中国今日实无学之患，而非中学西学偏重之患 -- 王国维 Re:我所知道的张五常（李俊慧）（之五）--道德风险作者:bear　　发表时间:2001年5月19日 16:34 我還是認為the cost of playing tennis is a institutional cost.是完全可接受的。我是想破了頭也不明白這個說法的不妥之處。看來這不並對影響理論的解釋力。個人喜好就不用爭了。一個人的行為的cost與 moral hozard都是看不到的，我傾向用cost,因為它存在，而我不確定是否有 moral hozard 這種東西。而且理論不宜繁。另外，cost 的用法不是象Ah sa說得那樣的。一些個較準的例子是：當每週買東西的機會少了，每次買東西的份量就多了。考試日期愈近，學生在圖書館的時問愈長(最後一兩天不是)。這可以被偽證。

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关键词：MORAL HAZARD Arrangements proportional Implications Compensation 讨论

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我心依旧 发表于 2004-10-4 15:44:00 |只看作者 |坛友微信交流群

Similarly, according to Cheung's definition, transaction cost is a composite variable. Depending on situations, it can consist of monitoring cost, commitment cost, information cost, searching cost, enforcement cost, contracting cost, advertising cost ....cost of fighting, cost of playing tennis, cost of talking, cost of kissing ...

Now we talk about the case of moral hazard.
For example, implication of owner-manager model is in this patern:
"Other things being equal,XYZ and equilibrium wage contract have this and that relation."
In this proposition, XYZ can be the information structure. It tells how the equilibrium contract depends on how observable manager's efforts is, how costly monitoring is, how many and how precise the signals owner receive ... All these are testable implications.

How can we explain the same phenomena by using the concept of transaction cost?

Probably, we can say:
"Other things being equal,transaction cost and equilibrium wage contract have this and that relation."
But, just like the concept of "水", transaction cost is a composite concept. Certain types of transaction cost is relevant to wage contract, but most are irrelevant. For example, we don't think increasing the cost of booking a tennis court will affect the wage contract!

So, how should we remedy? Probably we should divide transaction cost into transaction cost A and transaction cost B. Cost A is relevant and B is irrelevant. To identify the set A, we may choose "monitoring cost" is relevant, "information cost" is relevant, .... "talking cost" is irelevant, "kissing cost" is irrelevant ....

If this is the way to do, why do we bother to use the concept of "tramsaction cost" in this case, but not use the well defined concept of information strcture or monitoring structure?

-------------------------------
Note: I don't mean to say that the concept of transaction cost is useless. On the contrary, it is a bright idea back in the sixties. But after we have this broad idea, and we want to apply it to specific issues, we will need to "decompose" this definition into operational concepts such as monitoring structure/monitoring cost.

学无新旧，学无中西，中国今日实无学之患，而非中学西学偏重之患 -- 王国维

Re:我所知道的张五常（李俊慧）（之五）--道德风险
作者:bear　　发表时间:2001年5月21日 05:47

Ah sa　　:
我只是從未表達過我對道德風險的立場，張不用它，我可沒說張是對是錯，張怎麼用，不關我事。

無論用那個理論，都是要指出局限所在。information structure 真的更好被理解？我不知道。cost的麻煩是要找有關的局限，篩出無關的。這很繁，但我比不出那個方法更好。

LAWS DEFINE THE BOUNDARY OF FREEDOM.FREEDOM IS THE RIGHT TO CHOOSE.

Re:我所知道的张五常（李俊慧）（之五）--道德风险
作者:Ah sa　　发表时间:2001年5月22日 11:15

bear:
"無論用那個理論，都是要指出局限所在。information structure 真的更好被理解？我不知道。cost的麻煩是要找有關的局限，篩出無關的。這很繁，但我比不出那個方法更好。"

In economics, we always want to see how agents react to changes in constraint.We can describe the constraint in many differnet ways. Depending on situations, we can write it in terms of a total cost function, a bunch of specific cost functions, some feasibility sets, or any other detailed description of settings.

I am NOT saying the use of cost as a constraint is bad, but I attack on Cheung's broad definition of transaction cost.

Actually, in Moral hazard/game theory, we frequently use "cost" to model constraint.

An example:
Why do we have banks & financial market co-existing?
A standard "transaction-cost" answer is that:
"Because the transaction cost is this and that, so we have this type of arrangement in equilibrium."

The problem is: what type of transaction cost is relevant? I guess increasing the cost of booking a tennis court will not affect the equilibrium financial structure, no?

Therefore, to make this "transaction cost" arguement verifiable in operation, we may have to "refine" our set of transaction cost to, say monitoring cost (but not cost of talking, fighting, dancing,...).

But that's EXACTLY what we are doing using a moral hazard model!!!!!

In a moral hazard model of lending, because lenders have to pay some cost to observe borrowers' behavior (called costly state verification), we will have some special types of contract in equilibrium. (eg. debt contract)

In these moral hazard model, we can see how monitoring cost affect equilibrium lending arrangement. MOREOVER, we can derive effects of such exogenous variables as information flows and borrower & lender characteristics.

Is this a more complicated model than the "transaction cost" approach?
Yes, probably. But it can do much more and is much more well specified.

Let me repeat once more.

Transaction cost is a very bright idea when it is invented in the sixties (last century!). It may be a good concept (?) to study institutional change. But when it comes to specific issues like employment, lending, insurance ... it will become too broad in operation (we don't want to consider the cost of raising a baby in these cases). To make it operational, we design suitable constriants in different cases, sometimes expressed in cost, sometimes not. OK?!

But Cheung's comment that moral hazard model/game theory are tautological is very assertive and unreasonable!

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