The following is the scatterplot of the variables in Exercise 7 with regression lines added for each group:

The regression model is:
R-squared = 0.8398, Adjusted R-squared: 0.8265 SE = 1.3056 with 40 observations Variable Coefficient SE(Coeff) t-ratio P-value Intercept 28.6197 2.2856 12.5218 0.0000 Amount -0.1052 0.0108 -9.7115 0.0000 Teenagers -23.7696 3.0249 -7.8580 0.0000 Amount*
Teenagers 0.0938 0.0147 6.3694 0.0000

a) Write out the regression model.

b) In this regression, the variable Amount*Teenagers is an interaction term. How would you interpret its coefficient?

c) What null hypothesis can we test with the t-ratio for Amount*Teenagers?

d) Would you reject that hypothesis at 0.05? What do you conclude?

Transcribed Image Text:

Time (in minutes) 14 Time vs Amount 12 10 8 6 4 2 10+ 140 160 180 200 220 240 260 280 Amount (in milligram)