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Price elasticity of demand of CES

Economics Asked by stochastic learner on May 27, 2021

Anyone would like to help me show the following ( or a book/paper reference would be a great help)

" The price elasticity of demand is equal to $sigma$ for the demand function of CES preference, $d(p_i,I,P)=dfrac{p_i^{-sigma} I}{P^{1-sigma}}$, where $P=left(sum_{j=1}^N p_j^{1-sigma}right)^{dfrac{1}{1-sigma}}$ and $I=sum_{j=1}^Np_jx_j$."

The formula for the price elasticity of demand is given by $epsilon_i(p_i,I,P)=-dfrac{partial d(p_i,I,P)}{partial p_i}dfrac{p_i}{d(p_i,I,P)}$.

I have tried many times but couldn’t get the desired answer. Thank you very much in advance.

One Answer

Assuming that $p_i neq p_j$ you just apply the formula;

$$epsilon_i(p_i,I,P) =-dfrac{partial d(p_i,I,P)}{partial p_i}dfrac{p_i}{d(p_i,I,P)} = -left( frac{-sigma p_i^{-sigma-1} I}{P^{1-sigma}} right)frac{p_i}{frac{p_i^{-sigma} I}{P^{1-sigma}}} =sigma$$.

The way how you gave the problem neither $P$ or $I$ contain $p_i$ so you treat them as constants during differentiation.

Answered by 1muflon1 on May 27, 2021

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