戰昇的部落格

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.