IE 53o Homework 5.docx - IE 530 Homework 5 Answer 1 1 5.3 Discuss Type I and type II errors relative to the control chart What practical implication in

# IE 53o Homework 5.docx - IE 530 Homework 5 Answer 1 1 5.3...

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IE 530 Homework 5 Answer 1 1. 5.3 Discuss Type I and type II errors relative to the control chart. What practical implication in terms of process operation do these two types of errors have? Type I error relative to control charts is concluding the process is out of control when it is really in control and Type II error is concluding the process is in control when it is really out of control. If the type I error is present in a process operation, it means that we will assume that the process is in out of control and there is a presence of some assignable causes, so to deal with it we try to tamper the process and alter the nominal values and process parameters, this error will increase the cost incurred due to unnecessary process adjustment and changed control limits due to type I error. If type II error is present in a process operation, the process will not be able to detect the variation due to some assignable cause and there will be points lying outside the control limits which will not be detected it will result in more defective products during the production process. The defects will in turn increase the associated costs due to defective products. 2. 5.4 What is meant by a process that is in a state of statistical control? The statement that a process is in a state of statistical control means that no assignable or special causes of variation exist in the process or they have been removed by taking necessary actions. i.e The quality characteristic parameters like the mean and standard deviation lie between the specified upper control limit and lower control limit. 3. 5.7 What are warning limits on a control charts? Warning limits on control charts are limits that are limits specified between the upper and lower control limits. The usual action limits are at say. 3-sigma . When a point lies outside the action limit, a search is made for assignable cause and corrective actions are taken. Warning limits, say at 2-sigma, can be used to increase chart sensitivity and to signal process changes more quickly than the 3-sigma action limits. If one or more points fall between the warning limit and action limit, there can be a suspicion that process may not be operating properly. So possible actions like increasing the sampling frequency and sample size can be taken so that more information about the process can be obtained quickly and decisions can be made accordingly.

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ANSWER 2 1. 5.8 Discuss the rational subgroup concept. What part does it play in control chart analysis? The rational subgroup concept is used to maximize the chance for detecting variation between subgroups. This concept means that subgroups or samples should be selected in a way that if assignable causes are present, the chance for differences between subgroups will be maximized, while the chance for differences due to these assignable causes within a subgroup will be minimized. This maximizes the probability of detecting a shift from the control chart.
• Fall '97
• RAVINDRAN
• Control Chart, Process capability, UCL

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