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Unformatted text preview: 1 X bar & R chart Self Study Slides MGT 3360 Revised 04/10/08 See Technical Note 8 in the text for more information on Xbar & R charts 2 Formulas 3 General Procedure for Using R & Xbar Control Charts 1. Determine how many samples you have/need 2. Determine the size of each sample (n) you have/need 3. Take a random sample from the process (if you need to collect data) 4. Measure the quality characteristic 5. For Range Chart find: Ranges (R) and Rbar 6. Find UCL R and LCL R 7. Plot the data 8. For Xbar Chart find: Xbars and Xdoublebars 9. Find UCL X and LCL X 10. Plot the data 11. If the process is out of control then eliminate the causes, reconstruct the charts with new data and continue to monitor the process The following slides will lead you through the problem on the next slide. 4 Day 1 2 3 4 5 6 7 8 9 10 11 12 1 11 9 10 12 11 9 10 12 11 9 10 12 2 10 9 8 7 7 8 9 10 10 9 8 7 3 9 8 10 11 9 10 8 11 8 9 10 11 4 12 11 7 9 11 12 9 7 7 9 11 12 Range (R ) Mean (Xbar) Day 13 14 15 16 17 18 19 20 21 22 23 24 25 1 11 9 10 12 11 9 10 12 11 9 10 12 11 2 7 8 9 10 10 9 8 7 7 8 9 10 10 3 11 10 9 8 9 10 11 8 8 11 10 9 9 4 9 7 12 11 12 11 7 9 9 7 11 12 12 Range (R ) Mean (Xbar) Customer Service Example Problem Your company is concerned about the amount of time that your ambulance service takes to respond to a call. The data on the next slide was collected by sampling four emergency calls per day for five fiveday weeks. 5 1. Determine how many samples you have/need How many samples do we have? A sample is a group of observations taken at approximately the same time, usually once per day, or hour, or minute, etc The answer will be the same for the Xbar and R charts. 6 1. Solution There are 25 days when data was collected and thus there are 25 samples 7 2. Determine the size of each sample (n) you have/need What is our sample size (n)? The sample size is the number of observations in a sample 8 2. Solution The sample size (n) for each sample is 4. Each sample contained four observations. 9 Steps 3 & 4 were done for you 3. Take a random sample from the process (if you need to collect data) 4. Measure the quality characteristic 10 Day 1 2 3 4 5 6 7 8 9 10 11 12 1 11 9 10 12 11 9 10 12 11 9 10 12 2 10 9 8 7 7 8 9 10 10 9 8 7 3 9 8 10 11 9 10 8 11 8 9 10 11 4 12 11 7 9 11 12 9 7 7 9 11 12 Range (R ) Mean (Xbar) Day 13 14 15 16 17 18 19 20 21 22 23 24 25 1 11 9 10 12 11 9 10 12 11 9 10 12 11 2 7 8 9 10 10 9 8 7 7 8 9 10 10 3...
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 Spring '11
 AZEVEDO

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