Popular MechanicTM wants to determine if a new fuel additive improves gas mileage. The magazine hosts an online survey, asking car owners whether they use the fuel additive and what their car’s gas mileage is. Because car owners who use the fuel additive reported better gas mileages, the magazine concludes that the fuel additive works.
a. Describe the problems with the magazine’s study. Include in your description at least one possible lurking or confounding variable and identify which type it is.
b. Redesign the study so that it is a well-designed experiment.