Individuals Chart

Overview | How to | Example

 

 

Overview

The Individuals Chart is a control chart of individual observations. It is used to track the process level and detect signs of special causes when subgroup size is equals to 1. 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 > Individuals

  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 Lower Limit Bound, enter the bound on the lower control limit (Optional, Numeric)

  7. In Upper Limit Bound, enter the bound on the upper control limit (Optional, Numeric)

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

  9. In Method, choose the method of estimating sigma

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

  11. Check the various checkboxes to perform respective tests

  12. 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 > Individuals

  3. In Variable, select U - Response Time

  4. Click OK

 

Results & Interpretation

The ninth point lies outside the upper control limit which suggests a possible special cause. Further investigation is required and it is possible that it is the cause of that complaint.

 

 

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