Effectiveness of insect repellents. 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-per-use 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 are listed in the table below.
(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, 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, part c, and give the appropriate conclusion. Use α = .10.
(e) Repeat parts a-d if the dependent variable is maximum number of hours of protection (y).
