ECON Price Elasticity 之重大疑問

CHAN Kwan Ho

2007-06-12 5:16 am

Inelastic demand的定義是:
the % change in quantity demanded is smaller than the % change in price
理論上當價格提高的時候, total revenue 會 increase

那我舉一個例子:
假設當 good X 既 price 由 $10 提高到 $16 時
quantity demanded 就會由 20unit 跌到 10unit
那 % change in price = +60%
而 % change in quantity demanded = -50%
那麼 good X 的 demand 應該是inelastic

但計算 total revenue 時
原本是 = 10x20 = $200
加了價後 = 16x10 = $160
total revenue反而少了
為什麼???
請詳細解釋一下

回答 (1)

wagga

2007-06-12 10:03 am

✔ 最佳答案

因為你個Case 唔係Inelastic, 係elastic 先o岩.

首先, 你inelastic demand o既definition 係無錯o既. 而你錯o既原因係因為price elasticity 裡面o既 percentage changed 唔係就咁計.

own price elasticity of demand o既formula:
| % change in Q/% change in P | <-- notice about the absolute value
= | {(Q2-Q1)/[(Q2+Q1)/2]} / {(P2-P1)/[(P2+P1)/2]} |

**Notes: Q= Quantity; P=Price; therefore Q2= new quantity & Q1= original quantity

所以: % change in Q = -67%; % change in P= +46.2%
Own Price elasticity= | 1.44 |
當price elasticity 大過1, 就係elastic. {ΔQ=67%>ΔP=46.2%}
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簡單解釋點解要咁樣計change %:
mid-point analysis 係比一般(新-舊)/舊＊100% 更準確..因為真實情況o既數據裡面包括一定變化.
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conclusion: 記住elasticity 裡面o既% change 係要用mid-point analysis, 同埋條formula 係要absolute value.

希望你會明白我o既解釋啦

參考: 讀緊micro

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