6SQ ToolsWhat Is a Pareto Chart (80/20 Rule) and How Do You Use It?
If you’ve ever heard the phrase “the vital few and the trivial many,” you’re already close to understanding the Pareto chart. Named after economist Vilfredo Pareto—who observed in the early 1900s that roughly 80% of Italy’s land was owned by 20% of the population—this simple yet powerful tool helps teams focus their improvement efforts where they will have the greatest impact.
A Pareto chart is not just a bar chart. It’s a decision-making aid that combines bars and a cumulative line to visually separate the most significant causes of a problem from the less important ones. It is one of the seven basic quality tools taught in Lean and Six Sigma, and it appears in quality management standards and textbooks worldwide (e.g., ISO 9001 guidance on corrective action and the ASQ Quality Press body of knowledge).
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What It Is
A Pareto chart is a type of chart that contains both bars and a line graph. The bars, shown in descending order of frequency or cost, represent individual categories of causes or defects. The line represents the cumulative percentage of the total, usually plotted against the right-hand vertical axis.
The underlying principle is the Pareto principle, often called the 80/20 rule: in many situations, roughly 80% of effects come from 20% of the causes. For example, 80% of customer complaints may stem from just two or three defect types. The chart helps you identify that small set of “vital few” categories so you can allocate resources wisely, rather than spreading effort thinly across all possible causes.
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How It Works: Formula and Steps
No complex formula is required—the method is straightforward counting and arithmetic.
Step 1 – Define the problem and categories.
Decide what you are measuring (e.g., defect types, complaint reasons, delay causes) and list the categories.
Step 2 – Collect data over a defined period.
Count the frequency (or cost, or time) of each category. Use a check sheet for accuracy.
Step 3 – Sort categories in descending order.
Rank them from highest frequency to lowest.
Step 4 – Calculate the cumulative percentage.
For each category, compute:
```
Cumulative % = (Cumulative count up to that category / Total count) × 100
```
Step 5 – Draw the chart.
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A Worked Illustrative Example
Example data (illustrative only):
A small call center recorded 200 complaints over one month. The categories were:
Category | Count
Sort descending: Long wait (90), Incorrect billing (60), Rude staff (25), Technical issue (15), Other (10).
Cumulative percentages:
Drawing the chart, you would see that the first two bars (Long wait and Incorrect billing) reach 75% cumulative. Adding the third (Rude staff) crosses the 80% line. The “vital few” here are the first two categories—together they account for 75% of complaints. Fixing wait time and billing errors would resolve three-quarters of the problem, a far better use of effort than addressing all five categories equally.
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Common Pitfalls to Avoid
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Your Next Step
A Pareto chart is most powerful when used as part of a broader problem-solving cycle—define the problem, collect data, build the chart, then dig into root causes for the vital few. If you want to create one quickly without spreadsheet hassle, try the free Pareto chart tool at https://www.6sq.com/tools/pareto/ and turn your raw counts into a clear, actionable visual in minutes.
A Pareto chart is not just a bar chart. It’s a decision-making aid that combines bars and a cumulative line to visually separate the most significant causes of a problem from the less important ones. It is one of the seven basic quality tools taught in Lean and Six Sigma, and it appears in quality management standards and textbooks worldwide (e.g., ISO 9001 guidance on corrective action and the ASQ Quality Press body of knowledge).
---
What It Is
A Pareto chart is a type of chart that contains both bars and a line graph. The bars, shown in descending order of frequency or cost, represent individual categories of causes or defects. The line represents the cumulative percentage of the total, usually plotted against the right-hand vertical axis.
The underlying principle is the Pareto principle, often called the 80/20 rule: in many situations, roughly 80% of effects come from 20% of the causes. For example, 80% of customer complaints may stem from just two or three defect types. The chart helps you identify that small set of “vital few” categories so you can allocate resources wisely, rather than spreading effort thinly across all possible causes.
---
How It Works: Formula and Steps
No complex formula is required—the method is straightforward counting and arithmetic.
Step 1 – Define the problem and categories.
Decide what you are measuring (e.g., defect types, complaint reasons, delay causes) and list the categories.
Step 2 – Collect data over a defined period.
Count the frequency (or cost, or time) of each category. Use a check sheet for accuracy.
Step 3 – Sort categories in descending order.
Rank them from highest frequency to lowest.
Step 4 – Calculate the cumulative percentage.
For each category, compute:
```
Cumulative % = (Cumulative count up to that category / Total count) × 100
```
Step 5 – Draw the chart.
- Draw bars for each category in descending order (left to right).
- On the right axis, plot the cumulative percentage as a line.
- Typically, draw a horizontal reference line at 80% to visually separate the “vital few” (categories that reach the 80% line) from the “trivial many.”
---
A Worked Illustrative Example
Example data (illustrative only):
A small call center recorded 200 complaints over one month. The categories were:
Category | Count
- Long wait time | 90
- Incorrect billing | 60
- Rude staff | 25
- Technical issue | 15
- Other | 10
- Total | 200
Sort descending: Long wait (90), Incorrect billing (60), Rude staff (25), Technical issue (15), Other (10).
Cumulative percentages:
- Long wait: 90/200 = 45%
- Incorrect billing: (90+60)/200 = 75%
- Rude staff: (90+60+25)/200 = 92.5%
- Technical issue: (90+60+25+15)/200 = 95%
- Other: 100%
Drawing the chart, you would see that the first two bars (Long wait and Incorrect billing) reach 75% cumulative. Adding the third (Rude staff) crosses the 80% line. The “vital few” here are the first two categories—together they account for 75% of complaints. Fixing wait time and billing errors would resolve three-quarters of the problem, a far better use of effort than addressing all five categories equally.
---
Common Pitfalls to Avoid
- Using too many categories. If you have 20 bars, the chart becomes cluttered. Combine rare or unclear items into an “Other” category.
- Forgetting to sort descending. A Pareto chart that is not sorted loses its visual message.
- Ignoring the cost or severity dimension. Frequency is not the only measure. A rare defect that causes a $10,000 loss may matter more than a frequent $1 nuisance. Use cost or impact if that is your goal.
- Assuming 80/20 is a law. The ratio is a guideline, not a mathematical constant. Your data may show 70/30 or 90/10—the chart still works.
---
Your Next Step
A Pareto chart is most powerful when used as part of a broader problem-solving cycle—define the problem, collect data, build the chart, then dig into root causes for the vital few. If you want to create one quickly without spreadsheet hassle, try the free Pareto chart tool at https://www.6sq.com/tools/pareto/ and turn your raw counts into a clear, actionable visual in minutes.
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