125 Testing a new insecticide. Traditionally, people protect themselves from mosquito bites by applying insect repellent to their skin and clothing. Recent research suggests that peremethrin, an insecticide with low toxicity to humans, can provide protection from mosquitoes. A study in the Journal of the American Mosquito Control Association (Mar. 1995) investigated whether a tent sprayed with a commercially available 1% peremethrin formulation would protect people, both inside and outside the tent, against biting mosquitoes. Two canvas tents—

one treated with peremethrin, the other untreated—were positioned 25 meters apart on flat dry ground in an area infested with mosquitoes. Eight people participated in the experiment, with four randomly assigned to each tent.

Of the four stationed at each tent, two were randomly assigned to stay inside the tent (at opposite corners) and two to stay outside the tent (at opposite corners). During a specified 20-minute period during the night, each person kept count of the number of mosquito bites received.

The goal of the study was to determine the effect of both Tent type (treated or untreated) and Location (inside or outside the tent) on the mean mosquito bite count.

a. What type of design was employed in the study?

b. Identify the factors and treatments.

c. Identify the response variable.

d. The study found statistical evidence of interaction between Tent type and Location. Give a practical interpretation of this result.