Dr. Goodrich wanted to demonstrate that his tires were better than those of his competitor, Dr. Goodyear. From car registration and leasing records, he found 40 salespeople who drove the same model of automobile approximately the same number of miles per week. Anonymously, Dr. Goodrich hired an independent research assistant, who was unaware of the purpose of the study, to randomly assign to 20 of the sales people a new set of unmarked Goodrich tires, and to the other 20 a new set of unmarked Goodyear tires of the same price and quality. After six months and an average of 15,000 miles traveled by both groups, the assistant arranged for the salespeople to exchange tires. After another six months, and similar mileage, the assistant measured the amount of tread wear and reported that the Goodrich tires had actually worn more than the Goodyear tires.
(a) Identify the independent variable(s).
(b) Identify the dependent variable(s).
(c) Identify any confounding variable(s).

Dependent Variable is the variable being affected by independent variable(s). Independent Variable(s) are the causal variable, bring change in dependent variable.

Goodrich wants to demonstrate that his tires were better than those of his competitor (Goodyear). For that, he has got conducted an independent research on tires worn quality - brand wise & various factors affecting wear

Dependent Variable is the 'Tire tread wear '.
Independent Variables determining it is primarily brand : Goodrich / Goodyear ; secondarily - price, mileage, time etc

Confounding variable is an extraneous influence variable; that changes the relationship between independent & dependent variable, outcome of experimental research.

In this case : Individuals driving the vehicles could be a confounding variable. A particular person could wear out tire more than another person.