Pareto Chart

Definition Pareto Chart (Pareto Diagram)

A Pareto chart is a bar graph. The lengths of the bars represent frequency or cost (time or money), and are arranged with longest bars on the left and the shortest to the right. In this way the chart visually depicts which situations are more significant.

Ex:- Pareto Chart

When to Use a Pareto Chart

• When analyzing data about the frequency of problems or causes in a process.
• When there are many problems or causes and you want to focus on the most significant.
• When analyzing broad causes by looking at their specific components.
• When communicating with others about your data.

How To Make A Pareto Diagram

• STEP #1 - Determine the category classifications that you are going to use to group your defect data by. Use your check sheets to collect the data for the Pareto.

• STEP #2 - Decide on the time period to be used to record your information. One week, a month, etc. It is best to be consistent so that you have a standard to compare to if the data collection exercise is to be repeated again. You can't measure results achieved accurately without consistent measurement periods.

• STEP #3 - From the Check Sheet, total the occurrence of each item for the period measured. Each total will be represented by the length of a vertical bar, much like the Pareto chart example above.

• STEP #4 - (It is easier to keep your scale accuracy correct if you use graph paper). Draw horizontal and vertical axes on graph paper; or if no graph paper available, use a ruler to measure and draw evenly scaled vertical and horizontal lines that meet evenly (see figure 2 below).

 

Figure 2

• STEP #5 - Make your scale units at even multiples, such as 10, 20, etc. so as to have an even scale system (see figure 3 below).

 
Figure 3

• STEP #6 - Draw in the bars that correspond to the total numbers collected from your Check Sheet, starting on the far left, with the most frequent (highest number recorded) defective item. It is recommended that you leave a gap between each item bar for reading clarity. (Note: If you have several defective items with very small quantities, you can group them together in a category called "other", as long as their total is less than the previous bar heighth). Notice the figure 4 below.

 
Figure 4

• STEP #7 - Under the horizontal axis (line), label each of the bars so that you know which defect is represented by which bar.

• STEP #8 - Draw another vertical line and label the percentage scale in the same manner that you did on the left side (see figure 5 below)

 
Figure 5

• STEP #9 - Plot a dot for each item on the graph, starting from the left side, on or above the bar corresponding to the related percentage of defectives for each item. Once each dot is plotted, use a ruler and connect the line graph from dot-to-dot, as shown in the "Pareto example" up above.

• STEP #10 - Title the graph and briefly write the source of the data below the graph, that describes the data and method used to gather. Include all pertinent facts which will define the method of observation (for example, time period, production line, and whether this was before or after any modifications to the line). Recording this data on the bottom of your chart, will help further analysis as well as to provide a record of what was done on this date, for consideration in future studies.