Introductory Econometrics 4th Edition by Jeffrey Wooldridge

Exercise 1

Using the data in RDCHEM.RAW, the following equation was obtained by OLS:
(i) At what point does the marginal effect of sales on rdintens become negative
(ii) Would you keep the quadratic term in the model Explain.
(iii) Define salesbil as sales measured in billions of dollars: salesbil _ sales/1,000. Rewrite the estimated equation with salesbil and salesbil 2 as the independent variables. Be sure to report standard errors and the R-squared.
(iv) For the purpose of reporting the results, which equation do you prefer