The Pareto Chart

One of the first things new engineers are asked to do is to learn to prioritize tasks.  They are made aware early on to distinguish between the 'vital few' and the 'trivial many', which means that one has to focus on the few things that really matter, and not spend resources on the many others that have little or no impact. 

There was even a mathematical expression for it, known as the 80/20 rule, which states that 80% of all problem occurrences are due to only 20% of the types of problems encountered. Another variant of this rule states that for any problem, 80% of its occurrences are due to only 20% of all the causes. 

Thus, if one were to address a problem, the 20% of the causes that results in 80% of the problem (the 'vital few', so to speak) must first be identified and eliminated, before the rest are acted upon, if still necessary. The Pareto Chart is a very simple but effective tool for prioritizing problem causes, which is why it is widely used for problem-solving in the manufacturing industry. 

The Pareto Chart is basically a descending bar graph that shows the frequencies of occurrences or relative sizes of either: 1)  the various categories of all problems encountered, in order to determine which of the existing problems occur most frequently; or 2) the various causes of a particular problem, in order to determine which of the causes of a particular problem arise most frequently.  The problem categories or causes are shown on the x-axis of the bar graph.  

Aside from its main bar graph, the Pareto Chart may also include a line graph that indicates the cumulative percentage of occurrences at each bar of the bar graph.  This line graph, referred to as the 'cumulative percentage line', is used to determine which of the bars belong to the 'vital few' and which ones are relegated to the 'trivial many.'   Figure 1 shows an example of a Pareto Chart.

Bars that belong to the former group are those that account for bulk of the problems or problem causes encountered.  The last point of the line graph corresponds to the last bar of the bar graph (usually the 'Others' bar), and should correspond to 100% of the cumulative occurrences.

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See Also:  Ishikawa Diagram