Question

Which insect repellents protect best against mosquitoes? Consumer reports (June 2000) tested 14 products that all claim to be an effective mosquito repellent. Each product was classified as either lotion/cream or aerosol/spray. The cost of the product (in dollars ) was divided by the amount of the repellent needed to cover exposed areas of the skin *about 1/3 ounce) to obtain a cost-oer0use value. Effectiveness was measured as the maximum number of hours of protection (in half-hour increments) provided when human testers exposed their arms to 200 mosquitoes. The data from the report:

Insect Repellent                              Type   Cost/Use Maximum Protection
Away HourGuard 12            Lotion/Cream       $2.08      13.5 hours
Avon Skin-So-Soft       Aerosol/Spray      0.67                   0.5
Avon BugGuard Plus            Lotion/Cream       1.00                   2.0
Ben's Backyard Formula Lotion/Cream 0.75                  7.0
Bite Blocker                       Lotion/Cream         0.46                  3.0
BugOut                      Aerosol/Spray         0.11       6.0
Cutter Skinsations               Aerosol/Spray        0.22    3.0
Cutter UNscented    Aerosol/Spray     0.19               5.5
Musko1l Ultra6Hours            Aerosol/Spray     0.24                  6.5
Natrapel                         Aerosol/Spray      0.27                 1.0
Off! Deep Woods       Aerosol/Spray       1.77                  14.0
Off! Skintastic     Lotion/Cream    0.67              3.0
Sawyer Deet Formula          Lotion/Cream 0.36    7.0
Repel Permanone               Aerosol/Spray      2.75    24.0

a. Suppose you want to use repellent type to model the cost per use (y). Create the appropriate number of dummy variables for repellent type, and write the model.
b. Fit the model you wrote in part a to the data.
c. Give the null hypothesis for testing whether repellent type is a useful predictor of cost per use (y).
d. Conduct the test suggested in part c and give the appropriate conclusion. Use alpha=.10.
e. Repeat parts a-d if the dependent variable is maximum number of hours of protection (y).

Answer 1