Suppose you test the effectiveness of a new fuel additive. You run an experiment with 24 cars: 12 cars with the fuel treatment and 12 cars without. You input the dataset with 24 observations. The variable ‘mpg’ records the mileage rating and treats records 0 if the mileage corresponds to untreated fuel and 1 if it corresponds to treated fuel. Using rank- sum test in STATA, we get the results in Table 4.16:

a) What this result indicates?

b) How will you compute the Z value? (Mention the formula and the estimate)

c) Write the STATA command?

d) Is it a better test than the t- test? And why?