Many times you have data that can be best analyzed by dividing it into categories. A Pareto chart is one of the best tools for looking into categories.
A Pareto chart is a type of chart that contains both a histogram and a line graph, where individual values are represented in descending order by the histogram, and the cumulative total is represented by the line. The Pareto plot is used to answer the simple question: "Which data values are most important, and which are least important?"
The left vertical axis is the frequency of occurrence. The right vertical axis is the cumulative percentage of the total number of occurrences. The purpose of the Pareto chart is to highlight the most important among a set of factors. In quality control, it often represents the most common sources of defects, the highest occurring type of defect, or the most frequent reasons for customer complaints, and so on.
Why use a Pareto chart?
- Understanding the pattern of occurance for a problem
- Judging the relative impact of various parts of a problem (i.e. quantifying the problem)
- Tracking down the biggest contributors to a problem
- Deciding where to focus efforts
When to use a Pareto chart
- The problem under scrutiny can be broken down into categories
- You wish to identify the "vital few" categories to focus your improvement effort
Pareto Chart Features
- Use for categorical data
- Height of the bar represents the relative importance of that aspect of the problem
- Bars are arranged in descending order from left to right
- The bar for the biggest problem is always on the left hand side
- Height of the vertical axis represents the sum of all occurances (Not just the height of the tallest bar)
Execution
The Pareto Chart is plotted when the data is not suitable for a SPC Report. To generate a Pareto Chart select the data from the Name Value List and click the Report Icon at the top of the window.
Click the Report Icon to generate the Pareto report
Pareto Chart
The Pareto chart below illustrates a comments Name Value plot where product defect/failure comments were entered for the manufactured item. The Pareto plot illustrates clearly all types of defects in manufacturing and their importance.
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