Statistics for Business: Decision Making and Analysis, 3rd Edition

1. ... sales related to coupons considered in earlier sections. The data include n = 135 cases, of which 60 used coupons.

   Term	Estimate	Std Error	t-Statistic	VIF
   Intercept	47.236	10.253	4.607	—
   Family Size	18.038	7.362	2.450	4.324
   Coupon	− 22.383	5.251	− 4.263	3.250
   Coupon × Family Size	5.507	2.207	2.495	7.195

   1. What is the interpretation of the confidence interval for the coefficient of Coupon in the fitted model?¹¹

      ¹¹ The 95% confidence interval is − 22.383 − 2.00 × 5.251, which indicates that coupon users spend from $11.88 to $32.89 on average less, irrespective of family size (difference of intercepts).

   2. Should the interaction be removed and the model re-estimated?¹²

      ¹² No. The effect is statistically significant and the interaction must be ...