Unformatted text preview: DQ 1 What is a control chart? What are the grand mean, the UCL, and the LCL of a control chart for the mean? Why do you suppose ±3 standard errors are used in control charts and not two or even one standard error? Explain. Control chart is defined as a statistical analysis tool whose primary function is to check if a process is under control or not so in case process is found to be out of control we can take correct actions. Grand mean is defined as the mean of all sample means where as sample mean can be defined as when at periodic intervals, say n samples of product are taken and their measurements are taken the mean of these measurements calculated would me sample mean. Grand mean is said to be the standard value of a mean control chart or you can say that it is the central line of the mean control chart. UCL stands for upper control limit and LCL stands for lower control limit the process is said to be in between these limits if the process is out of these limits process is said to be...
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- Winter '11
- Statistics, Null hypothesis, Control Chart, Statistical hypothesis testing, Type I and type II errors, UCL