Question

Suppose that you are interested in the amount of wear that will occur on four different brands of automobile tires. In addition suppose that you have six different cars and six different drivers. You will conduct the following experiment: You will equip each car with one each of the four tire brands. Each of the six cars will be driven by the same driver for the same number of miles. After the required number of miles has been driven the amount of tread remaining on each tire will be measured. The following table lays out the data for this experiment. The blanks in the table will be filled in with the remaining tread on the tires.

	brand 1	brand 2	brand 3	brand 4
Car and driver 1
Car and driver 2
Car and driver 3
Car and driver 4
Car and driver 5
Car and driver 6

a) For this experiment what is the response?

b) For this experiment what is the factor? What are the levels for this factor?

c) For this experiment what are the blocks?

d) List possible nuisance variables for this experiment?

e) It is recommended that the brand of tire should be randomly assigned to the four possible positions on each car. Why is this important?

Answer 1

a) Response variable is the outcome to be measured or compared. Here, the response variable is the amount of wear that will occur on four different tyres of automobiles.

b) The factor for this experiment is the car and driver. There are 36 level (6 drivers *6 cars).

c) The blocks here, is the 4 brands-Brand A, brand B, Brand C and Brand D.

d) Possible nuisance variable is the speed of the car droven by the driver, as this might increase the variability of the overall score.

e) Random assignment is th eprimary criterion for any experiment, therefore, for the study to be an experiment, not observational one, one should randomize.