Why Model
Reason # 1: Intelligent Citizen of the World
Reason # 2: Clearer Thinker
Reason # 3: Understand and Use Data
Reason # 4: Decide, Strategize, and Design
•The model
–Assumptions, results, applications
•Technical Details
–Measures, Proofs (Easy, Medium, Hard)
–Practice Problems
•Fertility
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Intelligent Citizen of the World
Models Are Better Than We Are
Models Are Fertile【肥沃的;可繁殖的;丰富的;[物]能产生裂变物质的】
Models Make Us Humble
Many Model Thinkers Know Best
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Thinking More Clearly
Name The Parts
Identify Relationships
Work Through Logic
Inductively Explore
Understand Class of Outcome
Equilibrium【平衡，均势;平静】
Cycle
Random
Complex
Identify Logical Boundaries
Communicate
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Using and Understanding Data
Understand Patterns
Predict Point
Produce Bounds
Retrodict【追溯】
Predict Other
Inform Data Collection
Estimate【估计，预测;报价，预算书;评价，判断】 Hidden Parameters
Calibrate【校准;使标准化;使合标准;测量（枪的）口径】
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Using Models to Decide，Strategize，and Design
[Real Time]Decision Aids
{In the Monty Hall problem just described, should you stick with your original door or should you switch
After Monty eliminates one door, your chance of choosing the door with the prize remains one in three. The sum of probabilities has to add up to one. So the chance of the prize being behind one of the two doors you didn't initially select has to be two in three. Of those two doors, one is open and reveals nothing, so the other has a two in three chance of concealing the prize.}
Comparative Statics
Counterfactuals【反设事实】
Identify and Rank Levers
Experimental Design
Institutional Design【制度性；体制；机构的】
Help Choose Among Policies and Institutions
Peer Effect
{同群效应顾名思义，“同群效应”就是中国古语所谓“近朱者赤，近墨者黑”。它所指的是这样一种现象：一个人的行为不仅受到价格、收入等个体自身经济利益的激励影响，同时也会受到他周围的与他相同地位的其他人影响。}
{同群效应（peer effect），在一些经济学著作里，也被叫做“social capital”、“contagion”、“neighborhood effeets”或者“peer group effects”。}
Granovettor's[诺维特] Model
Aggregation{n. [地质][数] 聚合，聚集；聚集体，集合体}
Model
*N Individuals[n. [经] 个人；[生物] 个体（individual的复数）]
*Each has a Threshold[n. 入口；门槛；开始；极限；临界值]
-Tj for person j
-Join if Tj others join
{注释：如果没有person的threshold阀值为zero，那么这件事永远不会发生，
the tail's able to wag[摇摆；摇动；饶舌] the dog}
Collective Action
More Likely If:
-Lower Thresholds
-More Variation in thresholds
The Standing Ovation[热烈欢迎；大喝采] Model
Analyze：
Threshold to Stand: T
Quality: Q
Signal: S=Q+E
Initial Rule
-If S>T, Stand
Subsequent[adj. 后来的，随后的] Rule
-Stand if more X% stand
fertility 【n. 多产；肥沃；[农经] 生产力；丰饶】
The Identification Problem
Homophily[n. 同质性]
dynamic[
- adj. 动态的；动力的；动力学的；有活力的
- n. 动态；动力
- adj. 动态的；动力的；动力学的；有活力的
- n. 动态；动力]
Aggregation[n. [地质][数] 聚合，聚集；聚集体，集合体]
More is Different
Actions
Single Rule
Family of Rules
Preferences
Central Limit Theorem[n. [数] 定理；原理]