Pareto charts have data plotted in bar graph form and display the number of times each defect has occurred, in ascending order. They plot the relative contribution of each defect cause, and tell at a glance the largest causes.
The Pareto charting process consists of these steps;
• Decide how many categories to plot. This will be equal to the total number of bars.
• Draw an axis, which could be in either direction—horizontal vertical (y) axis. Label each category. Draw the vertical axis ^ percentage and total number of occurrences for each category shown for each bar.
• Use same-width bars, arranged from tallest to shortest.
• Add information: title, preparer, date, and so on.
The Pareto principle is similar to the “80-20” rule: 20% of the problems cause 80% of the defects. It could be used to focus on the probate causes of defects, as well as prioritize them. Ideally, a Pareto chart should have all small bars.
Figure 3.8 is a Pareto chart presentation of the percent reasons for
production downtime，showing the relative distribution of defect sources in terms of their occurrences.