Introductory Econometrics 4th Edition by Jeffrey Wooldridge

Exercise 17

For the population of firms in the chemical industry, let rd denote annual expenditures on research and development, and let sales denote annual sales (both are in millions of dollars).
(i) Write down a model (not an estimated equation) that implies a constant elasticity between rd and sales. Which parameter is the elasticity
(ii) Now, estimate the model using the data in RDCHEM.RAW. Write out the estimated equation in the usual form. What is the estimated elasticity of rd with respect to sales Explain in words what this elasticity means.