《微观经济学》清华大学(全套课件667P)

Two Very Common Modeling Assumptions
– Rational Choice (理性选择）: Each person tries to choose the best alternative available to him or her. – Equilibrium （均衡）: economic agents interact with each other, resulting in an equilibrium, in which each person reaches an optimal decision given others‟ decisions.
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Competitive Market Equilibrium
p
People willing to pay pe for close apartments get close apartments. People not willing to pay pe for close apartments get distant apartments.
Chapter One
The Market --- Appreciating Economic Modeling
The Purpose of this Chapter
To
begin to understand the art of building an economic model To begin to understand three basic elements of modeling in economics: – Purpose – Simplification through assumptions – Value judgment
Modeling Apartment Demand
The
lower is the rental rate p, the larger is the quantity of close apartments demanded p QD . The quantity demanded vs. price graph is the market demand curve for close apartments.
Market Demand Curve for Apartments
p
QD
Modeling Apartment Supply
Supply:
It takes time to build more close apartments so in this short-run the quantity available is fixed (at say 100).
Comparative Statics
Suppose
the price of distant apartment rises. Demand for close apartments increases (rightward shift), causing A higher price for close apartments.
Modeling Apartment Demand
Demand:
Suppose the most any one person is willing to pay to rent a close apartment is $500/month. Then p = $500 QD = 1. Suppose the price has to drop to $490 before a 2nd person would rent. Then p = $490 QD = 2.

An Illustration: Modeling the Apartment Market
Purpose:
How are apartment rents determined? Are rents “desirable”? Simplifying assumptions: – apartments are close or distant, but otherwise identical – distant apartments rents are exogenous (外生变量） and known – many potential renters and landlords
The Purpose of an Economic Model
The purpose of an economic model is to help provide precise insights (精 确的洞察力）on a specific economic phenomenon. Thus: – Different phenomena needs different model; – Simplification by assumption is necessary
pe 100
QD,QS
Comparative Statics （静态比较分析）
What
is exogenous in the model? – price of distant apartments – quantity of close apartments – incomes of potential renters. What happens if these exogenous variables change? Note： We are not analyzing the transition process or dynamic process.
Market Supply Curve for Apartments
p
100
QS
Competitive Market Equilibrium (竞争性市场均衡）
Quantity
demanded = quantity available price will neither rise nor fall so the market is at a competitive equilibrium.