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Week 5 DQ 3 - and LCL is lower control limit or lowest...

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Week 5 DQ 3 Please post your response to the following discussion question by clicking on Reply . Refer to Chapter 17 in the Applied Statistics in Business and Economics text. 1. What is a control chart? A control chart is a visual display that plots the values of a sample statistic over time through repeated observation. 2. What are the grand mean, the UCL and the LCL of a control chart for the mean? The grand mean is the average of all values (arithmetic mean) over a period of time. The overall sample mean or grand mean . y can be calculated either by summing all the observations and dividing by n or by taking a weighted average of the c sample means: . y = 1 n _ cj =1_ nji =1 yi j = 1 n _ cj =1 nj . yj The UCL is the upper control limit or highest value we’d expect for a process that is in control,
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Unformatted text preview: and LCL is lower control limit, or lowest possible value that we’d consider to indicate a process in control. 3. Why do you suppose ±3 standard errors are used in control charts and not two standard errors or even one standard error? I think any standard error could be used, because when using ±3 standard deviation =99.73%; it falls within the 3-sigma limits 4. Explain the four rules of thumb for identifying an out-of-control process. Rule 1- Single point outside 3 sigma. Rule 2- Two of three successive points outside 2 sigma on same side of centerline. Rule 3- Four of five successive points outside 1 sigma on same side of centerline. Rule 4- Nine successive points on same side of centerline...
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