Introductory Econometrics 4th Edition by Jeffrey Wooldridge

تمرين 3

Use the data in BARIUM.RAW for this exercise.
(i) Add a linear time trend to equation (10.22). Are any variables, other than the trend, statistically significant
(ii) In the equation estimated in part (i), test for joint significance of all variables except the time trend. What do you conclude
(iii) Add monthly dummy variables to this equation and test for seasonality. Does including the monthly dummies change any other estimates or their standard errors in important ways