Thinking Like an Economist 像经济学家一样思考Chapter 2Outline （概要） The Economist as Scientist 作为科学家的经济学家 The Economist as Policy Adviser 作为政策建议者的经济学家 Why Economists disagree 为什么经济学家意见会有分歧？The economic way of thinking . . . 经济学的思考方式 Involves thinking analytically and objectively. 包括分析性的客观的思考 Makes use of the scientific method. 使用科学的方法 Uses abstract models to help explain how a complex, real world operates. 使用抽象的模型来帮助解释一个复杂的真实世界是如何 运行的。 Develops theories, collects and analyzes data to evaluate the theories. 提出理论，收集并分析数据以检验理论The Economic Way of Thinking 经济学的思考方式钱颖一 (2002) Perspective （视角） Reference or Benchmark（参照系或基准点 ） Analytic Tools （分析工具）The Economic Perspective 经济学的视角About the Individual Behavior（关于个人行为 ） Scarcity （稀缺性） Opportunity Cost （机会成本） Tradeoff （权衡）The Economic Perspective 经济学的视角About Multi-Person Decisionmaking关于多 人决策： Equilibrium （均衡） Efficiency （效率） Win-Win （是否双赢）Reference/Benchmark 参照系/基准点 General Equilibrium (Arrow-Debreu) 一般均衡理论 Coase Theorem （科斯定理） Modigliani-Miller Theorem 莫迪格里安尼-米勒定理 Monetary Neutrality Theorem货币中性定理Economic Analytic Tools: Economic Models 经济学的分析工具：经济模型 The Economic way of thinking includesdeveloping abstract models from theories and the analysis of the models.经济学的思考方式包括建立 抽象的理论模型，并进行分析。 Uses two approaches （使用两种方法）Descriptive (reporting facts, etc.)描述性的（报告事实）Analytical (abstract reasoning)分析的（抽象推理）The Scientific Method 科学的方法 Observation （观察） Theory （理论） And More Observation （更多的观察）The Scientific Method 科学的方法 Theoretical Analysis: Explain how real world operates 理论分析：解释真实世界如何运行 Logic （逻辑 ）Proof （证据） Empirical Analysis: Analyze data to test the theory 经验分析：对数据进行分析以检验理论The Role of Assumptions 假设的作用 Economists make assumptions in order to make the world easier to understand. 经济学家做出假设为了使得这个世界更好理解 The art in scientific thinking is deciding which assumptions to make. 科学思考的艺术是决定做出哪些假设 Economists use different assumptions to answer different questions. 经济学家使用不同的假设来回答不同的问题The Economic Models 经济模型 Economists use models to simplify reality in order to improve our understanding of the world. 经济学家使用模型来简化事情以使我们更好地理解世界 。 Economic models omit many details to allow us to see what is truly important. 经济模型忽略许多细节以使我们可以关注真正重要的东 西。 All models are built with assumptions 所有的模型都建立在假设之上。 Two of the Most Basic Models两个最基本的模型 The Circular-Flow Model（循环流向模型） The Production Possibilities Frontier（生产可能性边界）The Circular-Flow Diagram 循环流转图 The circular-flow diagram is a visual model of the economy that shows how dollars flow through markets among households and firms. 循环流转图是一个直观的经济模型，表明了货 币是如何通过市场在居民和企业之间流动的。The Circular-Flow Diagram 循环流转图企业居民生产要素市场商品和服务市场SpendingRevenueWages, rent, and profitIncomeGoods & Services soldGoods & Services boughtLabor, land, and capitalInputs for productionThe Circular-Flow Diagram 循环流转图 Firms（企业） Produce and sell goods and services 生产并销售商品和服务 Hire and use factors of production 雇佣并使用生产要素 Households （居民） Buy and consume goods and services 购买并消费商品和服务 Own and sell factors of production 拥有并出售生产要素The Production Possibilities Frontier 生产可能性边界 The production possibilities frontier is a graph that shows the combinations of output that the economy can possibly produce given the available factors of production and the available production technology. 生产可能性边界是一个图形，表明在可行的生 产要素和生产技术给定的条件下，经济体所能 生产的产出的组合。Quantity of Computers ProducedQuantity of Cars Produced3,00001,0002,0007001,000300AB2,200600CDThe Production Possibilities Frontier 生产可能性边界Quantity of Computers ProducedQuantity of Cars Produced3,0001,0002,0002,200 A70060030001,000BCDProduction possibilities frontierThe Production Possibilities Frontier 生产可能性边界Concepts Illustrated by the Production Possibilities Frontier 生产可能性边界所阐释的概念 Efficiency （效率） Tradeoffs （权衡取舍） Opportunity Cost （机会成本） Economic Growth （经济增长）4,000Quantity of Computers ProducedQuantity of Cars Produced3,0002,000A70001,000E2,100750An outward shift in the production possibilities frontierThe Production Possibilities Frontier 生产可能性边界Correlation vs. Causality 相关性和因果关系 Economists usually illustrate the causality between two events using a graph with two variables in the coordinate system. 经济学家通常使用两个变量的坐标图来说明两个事件之 间的因果关系。 Ceteris Paribus, we claim that there is causality between variables if variable A cause variable B, and name A as the cause, B the effect. 在其他条件不变的情况下，如果A变量导致B变量，我们 就说A是原因，B是结果。Warning We call it correlation between variables if there are some reliable statistical relationship between variable A and variable B. 如果A变量和B变量之间有可信的统计关系，我们 就说这两个变量相关。 Sometimes we treat correlation as causality 有时候我们把相关性当成是因果关系。 BUT WarningCorrelation vs. Causality 相关性和因果关系Correlation maybe means causality相关性也许意味着因果关系 Correlation maybe means nothing相关性也许什么意义都没有 Omitted variable （遗漏变量） Reverse causality （倒因为果）WarningCorrelation vs. Causality 相关性和因果关系 Correlation means causality 相关性意味着因果关系WarningABP