Problem
To compare four brands oftires. one ofeach brand was randomly assigned to the four tire locationson each of 50 cars These tires were specially manufactured without any labels identifying the brand. After the tires had been on the cars for 30.000 miles. the researchers removed them and measured the remaining tread. They were not told which brand was which until the experment was over.
Explain why tire location on the vehile is a potential confounding variable and how randomization of the tire location helps minimize confounding.