Consider the following estimated equation that shows the impact of skipping class on college GPA: d colGPA = 1.39 (0.33)0.083 (0.026) skipped + 0.412 (0.094) hsGPA + 0.015 (0.011) ACT n = 141,R2 = 0.734, R2 = 0.563

2

where colGPA iscollegeGPA, skipped isthenumberoftimesskippingclass, hsGPA ishighschool GPA and ACT is American College Testing (ACT) scores.

(a) Can you reject the hypothesis H0 : hsGPA = 0.4 against the two-sided alternative at the 10% level? [5 marks]

(b) Can you reject the hypothesis H0 : skipped = 0.1 against the left-sided alternative at the 1% level? [5 marks]

(c) Suppose hsGPA and ACT were excluded from the model. The estimated equation becomes d colGPA = 1.04 (0.29)0.365 (0.193) skipped n = 141,R2 = 0.493, R2 = 0.211

Are hsGPA and ACT jointly signicant? [5 marks]