I-MR Chart

Overview | How to | Example

 

 

Overview

The I-MR chart is made up of an individuals Chart and Moving Range Chart. It allows you to track both process level and process variation at the same time and detect signs of special causes. The process standard deviation is estimated using average moving range with moving range equals to 2 as default.

 

 

How to

At the Excel Menu (For Excel 2007, go to Add-ins first)

  1. Choose ProcessMA > Control Charts > Variables Charts for Individuals > I-MR

  2. In Variable, select the column containing the data (Positive integer)

  3. In Historical Mean, enter the population mean, otherwise it will be estimated by the sample mean (Optional, Numeric)

  4. In Historical Standard Deviation, enter the population standard deviation, otherwise it will be estimated from the data (Optional, Numeric, >0)

  5. In Control Limit Multiples, enter the position to draw the upper and lower control limits. Multiple entries must be separated by commas (Optional, Numeric, >0, Up to 3 multiples)

  6. In I-Lower Limit Bound, enter the bound on the lower control limit for the individuals chart (Optional, Numeric)

  7. In I-Upper Limit Bound, enter the bound on the upper control limit for the individuals chart (Optional, Numeric)

  8. In MR-Lower Limit Bound, enter the bound on the lower control limit for the moving range chart (Optional, Numeric)

  9. In MR-Upper Limit Bound, enter the bound on the upper control limit for the moving range chart (Optional, Numeric)

  10. In Phase, select the column containing the phase indicators (Optional, >=2 distinct values)

  11. In Method, choose the method of estimating sigma

  12. In Moving Range Length, enter the number of observations used to calculate the moving range (Integer, >=2)

  13. Check the various checkboxes to perform respective tests

  14. Click OK

 

 

Example

You are the manager of a technical help division. There have been complains that response time were getting slow and erratic. You collected several measurements on response time and you want to run the I-MR Chart to evaluate the situation.

  1. Open data worksheet by choosing ProcessMA > Tools > Data

  2. Choose ProcessMA > Control Charts > Variables Charts for Individuals > I-MR

  3. In Variable, select U - Response Time

  4. Click OK

 

Results & Interpretation

The ninth point of the Individuals Chart lies outside the upper control limit which suggests a possible special cause on the process level. The process variation is stable as the data points are randomly distributed and lie within the control limits of the Moving Range Chart.

 

 

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