A consumer testing agency obtains four cars from each of six makes: Ford, Chevrolet, Nissan, Lincoln, Cadillac, and Mercedes. Makes 3 and 6 are imported while the others are domestic; makes 4, 5, and 6 are expensive 75 Exercise 4.1 Exercise 4.2 Exercise 4.3 Exercise 4.4 Problem 4.1 76 Looking for Specific Differences—Contrasts while 1, 2, and 3 are less expensive; 1 and 4 are Ford products, while 2 and 5 are GM products. We wish to compare the six makes on their oil use per 100,000 miles driven. The mean responses by make of car were 4.6, 4.3, 4.4, 4.7, 4.8, and 6.2, and the sum of squares for error was 2.25.

(a) Compute the Analysis of Variance table for this experiment. What would you conclude?

(b) Design a set of contrasts that seem meaningful. For each contrast, outline its purpose and compute a 95% confidence interval.