Question: Manufacturing and Product Development Shanghai Creative Material, Co. Ltd., makes plating tape for use on circuit boards, designed to be 4 mil thick. (A mil is equal to 0.001 inch: a milli-inch.) As part of quality control, every hour a random sample of 40 pieces of tape are carefully measured. If there is any evidence the thickness is different from 4 mil, then the entire process is stopped and the machinery checked and cleaned. Assume s = 0.05 mil and use a = 0.01.
a. Suppose the sample mean is x¯ = 4.014. Should the process be stopped?
b. Suppose the sample mean is x¯ = 3.979. Should the process be stopped?
c. Comment on the statistical and practical differences between the decisions in parts (a) and (b).