An automotive engineer was interested in the effect of four alternative rubber c

Question

An automotive engineer was interested in the effect of four alternative rubber compounds on the life of automotive tires. To carry out the study, five tires were manufactured from each of the four compounds and five automobiles were obtained for testing. With each automobile, the four tire types were assigned at random to the four wheels. Each automobile was driven for 40,000 miles and the amount of wear on each four tires was recorded.

a. What type of study is this, experimental, observational, or mixed? Why?

b. What is the basic unit of study?

c. What factors and factor levels are being studied here?

d. What type of study design is being implemented here?

e. Suppose that six compounds were under study instead of four. What type of study design is suggested?

Explanation / Answer

A. Experimental. You are running an experiment by choosing the tires, randomly assigning them, and then recording the wear. b. the basic unit of study is the amount of wear. c. The factor is the type of tire, and the level above that is car. d. Random study design with replication. e. If 6 tires were studied - obviously you can't put 6 tires on one car. I suggest using a random generator to randomly assign 4 of those 6 to a car - and then just use more cars so an adequate number of trials is acquired.

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