Use the data in MLB1 for this exercise.

(i) Use the model estimated in equation (4.31) and drop the variable rbisyr. What happens to the statistical significance of hrunsyr? What about the size of the coefficient on hrunsyr?

(ii) Add the variables runsyr (runs per year), fldperc (fielding percentage), and sbasesyr (stolen bases per year) to the model from part (i). Which of these factors are individually significant?
(iii) In the model from part (ii), test the joint significance of bavg, fldperc, and sbasesyr.