Minitab Quick Tip: Individuals Charts

October 20, 2018

An Individuals Chart is a tool to monitor variation in a process with continuous data over time.  Individuals charts can be used to monitor variables such as costs, temperature, number of invoices processed, amount of waste generated, and more.  When you create an Individuals Chart, Minitab calculates control limits for you.  The control limits are based on the data and tell us how much variation to expect.  Data points outside of the control limits indicate special cause variation.

 

Example 1

An operator wants to monitor the amount of time it takes to setup a machine for a process.  To do this, she plots the data using an Individuals Chart to see if the process is stable.

 

 

Based on the chart, there are no signals of special cause variation and the machine setup time is stable.

 

Example 2

A store manager wants to determine whether or not the daily sales at their store are stable and uses an Individuals Chart for analysis.

 

Based on the chart, the process is not stable.  Since one data point is outside of the control limits, the store manager should investigate this point to determine why it is different from the rest of the data.

 

Individuals Chart Creation

Before you create an Individuals Chart, make sure that your data is:

  • In time order

  • Continuous

  • Moderately normal

Once you have confirmed that an Individuals Chart is appropriate for your data, follow these steps:

  1. Enter your data in a Minitab worksheet

  2. Go to Stat – Control Charts – Variables Charts for Individuals - Individuals

  3. Double click on the column you want to use for the chart to bring it over to the Variables box

  4. Click OK

 

Note that these are basic instructions for creating Individuals Charts.  There are many options to customize your charts, which are not included here.  For additional information on Individuals Charts or questions about other Minitab tools, please contact us at meliora@myesc.com.

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