The U.S. National Highway Traffic Safety Administration (NHTSA) independently tests over 2,400 types of tires annually. In 2015, they issued over 900 recalls, affecting 51 million vehicles nationwide. Obviously, tire failure is a leading cause of accidents, injury, and death. The cost of poor quality can be in the hundreds of millions of dollars to the tire manufacturer due to lawsuits, liability claims, and the cost of recalls to fix the problem.
Tire manufacturers tests tires for tread wear under simulated road conditions. To study and control their manufacturing processes, company use x-bar and R charts.
Every week the quality control group of Goodman Tire & Rubber Co. randomly removes three radial tires from the production line and submits them to a standard test that simulates a variety of road conditions. Tread depth is measured before and after the test. The Workbook contains the data for tread wear, expressed in millimeters, resulting from the tests conducted with tires manufactured over the past 25 weeks.
Draw a histogram of the data. What can you conclude?
Construct x-bar and R charts for these data. Is the production process in control?
Sample Solution
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