A fleet of rental cars - all the same make, model, and year - has a mean fuel efficiency of 27 miles per gallon (mpg). A random sample of 54 cars are selected and the air filter of each is replaced with a new one. Let
be the population mean fuel efficiency score that would occur if every car's air filter were replaced. The air filter change is deemed effective if
A test is made of
Consider these possible conclusions:
i). The air filter changes are effective.
ii). The air filter changes are not effective.
iii). The air filter changes might not be effective.
Which of the three conclusions is best if
is not rejected?