Aside from the parameter, Problem 6.3.20 is different logically from Problems 6.3.12 through 6.3.19 in another important way. What is it? What justifiesthat difference for the other problems? Problem 6.3.20: We need to maintain strict control over the variability of the thickness of the coating on the coated paper which we manufacture. Our criterion for the variability is that the variance of the thick- ness should not exceed 0.3 mm. You are requested to set up a quality control procedure for this situation with five percent significance level. Problem 6.3.12: The purchasing department of your company must decide whether to continue with the same supplier for a certain machine part or possibly to switch to a new supplier. After some questioning, you find they're prepared to stay with the present supplier in the absence of strong evidence to back the new supplier's advertising claim that their part has a mean life of greater than 310 hours. The present supplier provides process control documentation showing a mean life of 285 hours for their part. You suggest to the purchasing department that they might want to control the risk of unnecessarily switching to a new supplier. Together, you decide to allow a one percent risk. Problem 6.3.19: The Internal Revenue Service is considering auditing all income tax returns which show a certain set of common characteristics on the assumption that those characteristics in combination flag an attempt at tax evasion. They have decided not to implement this new policy unless there is evidence at the ten percent significance level that more than 20% of such returns reveal attempts at evasion.
Aside from the parameter, Problem 6.3.20 is different logically from Problems 6.3.12 through 6.3.19 in another important way. What is it? What justifiesthat difference for the other problems?
Problem 6.3.20:
We need to maintain strict control over the variability of the thickness of the coating on the coated paper which we manufacture. Our criterion for the variability is that the variance of the thick- ness should not exceed 0.3 mm. You are requested to set up a quality control procedure for this situation with five percent significance level.
Problem 6.3.12:
The purchasing department of your company must decide whether to continue with the same supplier for a certain machine part or possibly to switch to a new supplier. After some questioning, you find they're prepared to stay with the present supplier in the absence of strong evidence to back the new supplier's advertising claim that their part has a mean life of greater than 310 hours. The present supplier provides process control documentation showing a mean life of 285 hours for their part. You suggest to the purchasing department that they might want to control the risk of unnecessarily switching to a new supplier. Together, you decide to allow a one percent risk.
Problem 6.3.19:
The Internal Revenue Service is considering auditing all income tax returns which show a certain set of common characteristics on the assumption that those characteristics in combination flag an attempt at tax evasion. They have decided not to implement this new policy unless there is evidence at the ten percent significance level that more than 20% of such returns reveal attempts at evasion.
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