How to Make a Control Chart Using Minitab

A control chart helps determine whether a certain process is stable.

Minitab is a statistical analysis package for the Windows operating system that can perform a wide range of analyses and manipulations to data sets, including the creation of a large selection of graphs and charts. One such graph is the control chart, which is used to determine whether a business or other process is operating “under control,” which means that fluctuations in the operation are due only to normal variability associated with that process.

Instructions

1. Setting Up the Data

   • 1
     Start Minitab and click the “Open” icon, which looks like an open folder, usually located at the far left of the toolbar at the top of the window. Browse to the folder containing your data, then double-click the file to open it.
   • 2
     Check that the data is ordered correctly. Dedicate one column to dates or times and another column to the output variable, whether they're delivery dates, production line output or any other data you choose to analyze. You may have more than one entry per date.
   • 3
     Sort the date column into chronological order if it's not already sorted. Click “Data” and “Sort.” From the list of columns on the left, double-click your time column, then your output variable column. Click inside the first “By column” box, then double-click the date column from the list on the left again. Then click “OK.” If entries in your time column are repeated more than once, continue to “Creating a Chart for Subgroups.” Otherwise move on to “Creating a Chart for Individuals.”

   Creating a Chart for Subgroups

   • 4
     Click “Stat,” “Control Charts,” “Variables Charts for Subgroups.” If you have less than five entries per time, click “Xbar-S.” Otherwise, click “Xbar-S.”
   • 5
     Double-click your time column from the list on the left, click inside the “Subgroup sizes” box and double-click the output variable option from the list of columns on the left.
   • 6
     Click “OK” to create the chart.

   Creating a Chart for Individuals

   • 7
     Click “Stat,” “Control Charts,” “Variables Charts for Individuals” and “I-MR.”
   • 8
     Double-click your output variable. Then click “Scale.” In the pop-up window, click “Stamp" and double-click the time column.
   • 9
     Click “OK,” then “OK” again to create the chart.