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Su Bukisa potete leggere un articolo dal titolo: "Problem Solving Techniques: Pareto Diagram Analysis".

Questa è la versione tradotta in italiano con il traduttore automatico di Google.

A Pareto Diagram is a bar chart organized with the target bar to the left and the smaller bars to the right in order of frequency. A problem solving team uses a Pareto Diagram to discover what type of categories relate to the problem and allows them to focus on the most important items to handle with. A useful Pareto Diagram shows 20% of the inputs are the cause of 80% of the problems with dependent process outputs (20-80 pattern). Therefore, a Pareto Diagram is a very powerful tool in problem solving.

In constructing a Pareto, one must decide on the process you want to know more about. You should be able to choose the causes or problems that will be monitored, compared and rank ordered by; brainstorming (what are the issues?) and using the existing data (what issues surfaced in the last month?). Then, you should be able to choose the most meaningful unit of measurement (frequency, cost or both). Select a time period for the study which is long enough to accurately represent the situation. Look at volume and variety in the data and make sure that the scheduled time is “typical” to allow for seasonality or different work patterns within a given day or week. Use a cheek sheet or other method to gather “real time” or historical data on each problem category. Label the axis, the chosen measurement units (e.g. frequency, cost) are shown on the vertical axis while the chosen problem categories are shown on the horizontal axis. With this, you should be able to construct the bar graph. List the problem categories in descending order from left to right on the horizontal axis. If desired, convert the frequency or cost for each item into % of the total. Calculate the percentages for the items from left to right, and cumulate from left to right. Plot the cumulative percentages.

To interpret a Pareto Diagram, one may say that the vertical axis shows the counts (or cost) while the horizontal axis shows the items rank ordered from left to right. And the bars are the account of the 80% of the problem. Also, the cumulative percentages shows how much of the total problem will be fixed by addressing the vital few.

A Pareto Diagram can be use in the following problem situations:

A major cause breakdown (Drill-down Pareto), this shows the tallest bar broken down into sub-causes in a second.
Before and after situation. This shows new bars drawn side-by-side with the original to show the effect of change. The sample sizes of before and after situation must be identical to have a common reference and be able to examine more clearly the effect of the implemented action.
Change source data. Data is collected on the same problem from different source locations, equipment, etc. and shown side-by-side on the Pareto Diagram.
Change measurement scale. The same data is used, but measure differently. Typically the cost and frequency are alternated.
When using Pareto Analysis as a problem solving tool, one must remember that they are typically used to prioritize competing or conflicting problems and to distinguish the “vital few” from the “trivial many”. Pareto diagrams determine which several classifications have the most count or cost associated with them. The base data gathered must be in term of either counts or cost therefore do not use terms that can’t be added, such as yields or error rates. And lastly, if the first one doesn’t show a 20-80 pattern, then consider the problem and try again.