How to make a Pareto chart
- Collect the data over a representative period, for example a month of scrap records, customer complaints or downtime reasons.
- Paste
category; countlines, or just the category of each event on its own line. Duplicate categories are added up. - Read the vital few from the summary and the highlighted bars.
After the Pareto
Take the largest bar and ask why it happens. A fishbone diagram helps to list possible causes in a structured way, and an FMEA helps to prevent the problem from coming back. Repeat the Pareto after the fix: the old top bar should have shrunk.
Frequently asked questions
›What is the 80/20 rule in a Pareto chart?
The Pareto principle says that a small number of causes, roughly 20 %, are responsible for most of the effect, roughly 80 %. The chart sorts categories from largest to smallest and adds a cumulative line so you can see where the 80 % is reached.
›What are the vital few?
The vital few are the categories needed to reach the cut-off, usually 80 %, including the one that crosses it. They are where improvement effort pays off most. The remaining categories are the useful many.
›Can I weight categories by cost instead of count?
Yes. Enter the cost (or scrap time, or any other weight) as the number instead of the count. A cost-weighted Pareto often ranks problems differently from a frequency Pareto.
›Should I have an "Other" category?
Group rare categories into Other to keep the chart readable, but if Other becomes one of the largest bars, split it up because it hides real problems.