Pareto Charts and Six Sigma

Six Sigma is a more comprehensive version of the PDCA cycle that was developed by Motorola Corporation many years after Deming first developed the PDCA cycle.

Six Sigma is made of up five phases, known as DMAIC:

Define:  Identify the best projects and define each project’s scope and goals clearly, i.e. “Improve rolled throughput yield from 85% to 90% in the fuel pump assembly area.”

Measure:  Understand historical performance and ensure that the measurement system (at the metric level or product/process characteristic level) is sound.

Analyze:  Understand the top causes contributing to unwanted variation.

Improve:  Eliminate or sufficiently control the top causes identified in the Analyze phase, to achieve the project objective.  Demonstrate that the new level of control will deliver predicted results.

Control: Implement long-term process controls, as part of the quality system, to sustain the positive changes made in the Improve phase.

Pareto Analysis in the Define Phase

Effective Six Sigma projects are narrowly focused and have clearly defined goals in terms of results and project completion time.  To ensure that project definitions are not too broad, an initial Pareto analysis of the top level metric is conducted to define a project that covers one or more Pareto categories.  For example, if a leadership team is seeking to reduce overall scrap by a significant percentage, a review of the top-level Pareto chart could create two or more Six Sigma projects focused in the highest scrap-producing areas in the plant.


how a pareto chart is used to help narrow project selection in Six Sigma

Pareto charts help with Six Sigma project definition


Pareto Analysis in the Analyze Phase

In cases where Six Sigma teams are working on problems that have multiple, easily captured top level causes, Pareto charts are very useful in further focusing the team on the biggest opportunities.  For example, a warranty improvement project would benefit from a Pareto chart showing the top level reasons for warranty returns, so the team can focus its efforts for maximum results.


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