※ 引述《ninmit (silent all the years)》之铭言： : 看到上面的讨论串, 突然想起一个总体的一个作业题目, 想和各位先进请益...... : 在 Ramsey 模型中, 或者是大学部的 Barro 课本, 大概都会有一个假设 - 代表性个人. : 我记得当年问过强者我总体老师, 我问他说: 为什麽代表性个人可以假定加总成整个经济 : 体系. 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, 另一个问题是, 代表性个人的偏好是否就为全体社会的偏好 @@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. -- These questions are good and important. -- 社会主义救台湾 三民主义解放中国 ※ 编辑: economist 来自: 70.80.37.233 (05/09 11:21)