像经济学家一样思考问题 | 武大经济学课

总结于武大经济学课的经济学家的研究方法

一：Thinking like as economist

• Every field of study has its own way of thinking ：

  • Mathematicians： axioms(积分)， integrals， vector ，spaces (向量空间)
  • Psychologists：ego(自我)， id(身份)， cognitive dissonance(认知偏离)
  • Lawyers：venue(犯罪现场)， torts， promissory estoppel (禁止悔供)
  • Economists：Supply(供给)， opportunity cost(机会成本)， elasticity，consumer surplus， demand，comparative advantage(比较优势)，deadweight loss(无谓亏损)

• The Economist as Scientist

  • Economists try to address their subject with a scientist objectivity；
  • This method of inquiry is as applicable to studying a nation’s economy as it is to studying the earth’s gravity or a species’ evolution；

• The scientific method: Observation, theory, and more observation

  • rapid increase of prices → make observations →develop a theory →assert a link between high inflation and printing too much of money →to test the theory, economists collect and analyze data →find out the correlation between these two → come to their conclusions

• The Role of Assumptions

  • Economists make assumptions for the same reason: Assumptions can simplify the complex world and make it easier to understand.

二：Economic Models

• Our first model: the circular-flow diagram
  present a visual model of the economy, called the circular-flow diagram. Firms produce goods and services using inputs such as labor, capital (buildings & machines) and land. These inputs are called the factors of production.Households own the factors of production and consume all the goods & services that the firms produce.

Fig. 1 the circular-flow diagram

• Households and firms interact （相互作用，相互影响） in two types of markets.
  In the market for goods and services, households are buyers and firms are sellers. In the market for the factors of production, firms are buyers and households are sellers.

• Our second model: the production possibilities frontier
  生产可能性边界，简称PPF(或是production-possibility boundary)。用来表示经济社会在既定资源和技术条件下所能生产的各种商品最大数量的组合，反映了资源稀缺性与选择性的经济学特征。通常为两种商品的生产可能性比较。在坐标轴上表示出的图形为生产可能性曲线，也可称为转换线(production possibilities curve )。
  The PPF is a graph that shows the various combination of output-----in this case, cars and computers---- that the economy can possibly produce given the available factors of production and the available production technology that firm can use to turn these factors into outputs.

Fig. 2 production possibilities curve

The PPF show the combinations of output ---- in this case, cars and computers----that the economy can possibly produce. The economy can produce any combination on or inside the frontier. Points outside the frontier are not feasible given the economy’s resources

三：What causes the PPF shift?

• Technological advance
• More resource
• Better resource
• Government policies
• Trade with other countries

四：Three basic assumptions underlie the production possibilities frontier model

• Fixed resources
• Fully employed resources.
• Technology unchanged.

五：The production possibilities frontier shift outward

• The PPF shows the tradeoff between the production of different goods at a given time, but the tradeoff can change over time.

Fig. 3 The production possibilities frontier shift outward

If a technological advance in the computer industry raises the number of computers that a worker can produce per week, the economy can make more computers for any given number of cars. As a result, the PPF shifts outward, as in Fig.3. Because of this economic growth, society might move production from point A to point E, enjoying both more computers and more cars.