Exercise

# The effect of multiple dummies on sales

The brewery also distributed manufacturer coupons, offering price reductions for **Hoppiness**. A third marketing strategy was to combine display and coupon activity to increase volume sales.

This time, you will calculate the mean of `log(SALES)`

for each `DISPLAY`

, `COUPON`

, and `DISPLAYCOUPON`

level combination by using the function `aggregate()`

. You can do this by successively **adding** the variables to the formula argument.

To describe the effects of coupon and display activity, you again estimate a linear response model by using the function `lm()`

. As usual, you investigate the coefficients.

Instructions

**100 XP**

- Calculate the mean of
`log(SALES)`

for each`DISPLAY`

,`COUPON`

, and`DISPLAYCOUPON`

level combination. - Explain
`log(SALES)`

by`DISPLAY`

,`COUPON`

, and`DISPLAYCOUPON`

. Use the function`lm()`

and assign the result again to an object called`dummy.model`

. - Obtain the coefficients of the
`dummy.model`

by using the function`coef()`

.