A Pareto chart is a bar graph that depicts the relative frequency of defects in a process. This type of graph is like a bar chart; however, the data are ordered from the most frequently occurring to the least frequent. This type of chart was named for the Pareto principle, also known as the 80/20 rule that states that 80 percent of your time is spend on problems that are only occurring 20 percent of the time. Minitab is a statistical software package that automates the calculation of Pareto charts.
Enter the categories of defects into Minitab in the form of a column. If, for example, you wanted to create a Pareto chart of problems you are having with your cell phone, your data would look like this:
Problem Dropped calls Lack of service Failure to charge Failure to send text Failure to receive text
Create a second column, immediately to the right of the first column. This column will contain the frequency of occurrence for each of the categories listed in the first column. The data would look like this:
Occurrence 10 23 45 67 89
Use the left mouse button to select the “Stat” option from the main menu. A submenu will drop down; select the “Quality Tools” option. Another submenu will appear. Choose the “Pareto Chart” option. A Pareto chart box will appear.
Choose the data to plot for the Pareto chart by double-clicking on options in the white box that list the data available for the analysis. In this example the choices will include:
C1 Problem C2 Occurrence
There will be a sentence to complete that starts with: “Defects or attribute data in” -- there is a blank white box to the right of this text. Put the cursor in the box by clicking in the box with the left mouse button. Next, double-click on the column of data from the white box that has your categories -- in this example, the C1 Problem column. Double-clicking on this choice will automatically insert this text into the “Defects or attribute data in” box.
Put the cursor in the box next to the “Frequencies in” heading. Then select the column of data that has the frequencies of the defects from the white box -- in this example, the “C2 Occurrence” data. Double-click on the words “C2 Occurrence” to put these terms into the “Frequencies in” box.
Click on the “OK” button with your left mouse button. Minitab will produce the Pareto chart. Change the title by double-clicking on it with the left mouse button and entering a new title.
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