A researcher would like to study the relationship between average fuel economy (measured in miles per gallon) and fuel type (premium, regular unleaded, and E85). He randomly selects 90 vehicles of various makes and models, including compact cars, full-size cars, and trucks. All of the selected vehicles have been driven less than 6,000 miles before the experiment. a) Does this experiment use a control group? Explain.
b) Suppose the researcher would like to use a completely randomized design. Explain how the researcher should assign the 90 vehicles to the three fuel types.
c) An advisor to the researcher suggests using a randomized block design. Should the researcher block on type of vehicle (compact cars, full-size cars, and trucks) or number of miles previously driven (0–2,000 miles; 2,000–4,000 miles; and 4,000–6,000 miles)? Explain your choice of blocking variable.