Manufacturing and Product Development
In residential and commercial buildings, the thickness of window glass varies according to the width of the window. Wider windows require thicker window panes. As part of quality control, a manufacturer randomly samples windows and carefully measures the width of each (in millimeters). Consider the data in the following table.
a. Find a 99% confidence interval for the true variance of window thickness for each window width category. Assume normality.
b. Suppose a process is considered "in control" if the variance is 0.02 mm (or less). Is there any evidence to suggest any of the three processes is out of control?