從社會偏好到代表性個人... 我的不解處 - 經濟

※ 引述《ninmit (silent all the years)》之銘言：
: 看到上面的討論串, 突然想起一個總體的一個作業題目, 想和各位先進請益......
: 在 Ramsey 模型中, 或者是大學部的 Barro 課本, 大概都會有一個假設 - 代表性個人.
: 我記得當年問過強者我總體老師, 我問他說: 為什麼代表性個人可以假定加總成整個經濟
: 體系.

The assumption of representative agent is merely technical.

Economists made this assumption during early years because they didn't know

how to deal with heterogeneity.


Nowadays we sometimes make this assumption when (1) the questions we try to

answer do not involve income/wealth distributions or any kind of heterogeneity;

or (2) the implications from a model with representative agent are robust to

different income/wealth distributions.

In particular, we could safely assume an representative agent if the

Aggregation Theorem holds. (This should be Macro 101 for any Ph.D. student

I assume.)


The Aggregation Theorem specifies the sufficient conditions under which

the aggregate (macro) variables derived in the model with a representative

agent are identical to those derived in a full-fledged model with

heterogeneous agents.


It is (almost) always true that when those sufficient conditions hold,

an individual's decision rules (for example, regarding how much to consume

or how much to save) are LINEAR in individual state variables (for example,

individual asset holdings or savings). This implies that all the aggregate

variables (for example, aggregate consumption level and aggregate saving) are

independent of the distributions of different types of agents.


As an example, in the basic Lucas-tree model (in which there is a complete

market with no borrowing constraint, and the utility function is CRRA),

the Aggregation Theorem holds, so we are free to assume a representative

agent.


: 或者, 另一個問題是, 代表性個人的偏好是否就為全體社會的偏好 @@a

This, in fact, is a different question.


Before we talk about the aggregate preferences of the society we have to

specify (or make assumptions about) how individual preferences are aggregated.


A common way of doing that is to aggregate individual preferences by simple

majority rule.


Keep in mind that preferences are orderings.

We say a society (a group of individuals) prefers alternative A to B

under simple majority rule if and only if there exists a majority of

individuals who prefer alternative A to B.


It is not unusual that the "representative agent" has a different policy

preference from that of the "society". For example, in Meltzer and Richard's

seminal AER paper on the size of government, the "representative agent" is

the average person in the society while the aggregate policy preference of

the society is identical to that of the median person.



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These questions are good and important.



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社會主義救台灣
三民主義解放中國
※ 編輯: economist 來自: 70.80.37.233 (05/09 11:21)