Fuel efficiency Wayne Collier designed an experiment to measure the fuel efficiency of his family car under different tire pressures. For each run, he set the tire pressure to either 28 or 32 psi and then measured the miles driven on a highway (I-95 between Mills River and Pisgah Forest, NC) until he ran out of fuel using 2 liters of fuel each time. He also used two different types of gasoline (regular and premium).

To run the experiment he made some alterations to the normal flow of gasoline to the engine. In Wayne’s words,

“I inserted a T-junction into the fuel line just before the fuel filter, and a line into the passenger compartment of my car, where it joined with graduated 2 liter Rubbermaid bottle that I mounted in a box where the passenger seat is normally fastened. Then I sealed off the fuel-return line, which under normal operation sends excess fuel from the fuel pump back to the fuel tank.”

a) Identify the factors and the levels in the experiment.

b) How many times would he need to drive to make sure all treatments are represented and each treatment combination is replicated?

c) For simplicity, he wants to run all the regular gasoline runs first. Explain why this might not be a good idea.

What would you suggest?

d) If he wanted to enlist a friend to use his car to double the number of runs by replicating all treatments, what kind of new factor would he be introducing?