今天是 Week 5,課程內容涵蓋了彈性 (Elasticity)、Slutsky Equation、以及Endowment Model。以下分主題整理:
一、彈性 (Elasticity)
1. 收入彈性 (Income Elasticity)
- 測量需求量對收入變化的敏感程度。
- 彈性範疇:
- 必需品 0 < η 1
- 奢侈品 η > 1
- 劣等財 η < 0
2. 自價格彈性 (Own Price Elasticity)
- 測量需求量對自身價格變化的敏感程度,分為
- 富有彈性:ε> 1
- 無彈性:ε<1
- 單一彈性:ε= 1
3. 交叉價格彈性 (Cross Price Elasticity)
- 測量商品1需求量對商品2價格變化的敏感程度:
- 判定關係:
- ε_12 > 0:替代品 (e.g., 蘋果 vs 梨)
- ε_12 < 0:互補品 (e.g., 咖啡 vs 奶精)
4. 替代彈性 (Elasticity of Substitution)
- 衡量兩商品需求比例對相對價格變化的敏感性:
二、Slutsky Equation
1. 價格效果分解 Price Effect Decomposition
- 將價格變化對需求量的影響分為兩部分:
- 替代效果:由相對價格變化導致的需求改變。
- 所得效果:由購買力變化導致的需求改變。
- 替代效果總是負值,而所得效果可能為正或負。
2. 需求曲線與法則
- 正常財:需求曲線向下 (價格上升,需求下降)。
- 劣等財:價格效果可能不明確,甚至出現向上需求曲線 (吉芬財)。
三、Endowment Model
1. 禮物與預算約束
- 消費者的收入來自於自身所擁有的商品銷售。
2. 價格變化與效用影響
- 對於淨賣家,價格上升通常提升效用;而淨買家則可能遭遇效用降低。
3. 應用:勞動供給模型
- 消費者選擇在消費與閒暇之間平衡,面對工資與商品價格的預算約束:
Today is Week 5, and the lecture covered Elasticity, Slutsky Equation, and the Endowment Model. The main points are summarized below:
A. Elasticity
1. Income Elasticity
- Measures the sensitivity of demand to changes in income.
- Elasticity categories:
- Necessities: Demand increases with income, but at a limited rate.
- Luxuries: Demand increases rapidly as income rises.
- Inferior goods: Demand decreases as income increases.
2. Own Price Elasticity
- Measures the sensitivity of demand to changes in its own price, categorized as:
- Elastic: Demand is highly sensitive to price changes.
- Inelastic: Demand is not significantly affected by price changes.
- Unit Elastic: The percentage change in demand equals the percentage change in price.
3. Cross-Price Elasticity
- Measures how the demand for one good responds to price changes in another good:
- Substitutes: For example, apples and pears, where a price change in one affects the demand for the other.
- Complements: For example, coffee and cream, where their demands are interdependent.
4. Elasticity of Substitution
- Evaluates the sensitivity of the ratio of demand for two goods to changes in their relative prices, helping understand consumer preference shifts.
B. Slutsky Equation
1. Price Effect Decomposition
- The impact of price changes on demand can be broken down into:
- Substitution Effect: Changes in demand caused by relative price changes.
- Income Effect: Changes in demand caused by changes in purchasing power.
2. Demand Curve and the Law of Demand
- Normal Goods: Demand decreases as prices rise, aligning with the downward-sloping demand curve.
- Inferior Goods: In some cases (e.g., Giffen goods), demand may increase as prices rise.
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C. Endowment Model
1. Endowment and Budget Constraint
- A consumer's income comes from selling their owned commodities, extending the traditional fixed income model.
2. Price Changes and Utility Impacts
- For net sellers, a price increase usually enhances utility, while for net buyers, utility may decrease.
3. Application: Labor Supply Model
- Explores how consumers balance consumption and leisure, analyzing the effects of changes in wages and commodity prices on consumption behavior.