pany’s Bright Side laundry detergent (S) are related to Vanguard’s own advertising ex-
penditure (A), as well as the combined advertising expenditures of its three biggest
rival detergents (R). The marketing director collects 36 weekly observations on S, A,
and Rto estimate the following multiple regression equation:
where S, A, and R are measured in dollars per week. Vanguard’s marketing director is
comfortable using parameter estimates that are statistically significant at the 10 percent
level or better.
a. What sign does the marketing director expect a, b, and cto have?
b. Interpret the coefficients a, b, and c.
The regression output from the computer is as follows:
Dependant variable: S R=Square F-Ration P-value F
P-Value on F
Observations: 36 0.2247 4.781 0.0150
Variable Parameter Standard T Ratio P-Value
Intercept 175086.0 63821.0 2.74 0.0098
A 0.8550 0.3250 2.63 0.0128
R -0.284 0.164 -1.73 0.0927
c. Does Vanguard’s advertising expenditure have a statistically significant effect on the
sales of Bright Side detergent? Explain, using the appropriate p-value.
d. Does advertising by its three largest rivals affect sales of Bright Side detergent in a
statistically significant way? Explain, using the appropriate p-value.
e. What fraction of the total variation in sales of Bright Side remains unexplained?
What can the marketing director do to increase the explanatory power of the sales
equation? What other explanatory variables might be added to this equation?
f. What is the expected level of sales each week when Vanguard spends $40,000 per week
and the combined advertising expenditures for the three rivals are $100,000 per week?
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