Six Sigma

About Six Sigma

Six Sigma is a disciplined, data-driven approach and methodology for eliminating defects (driving toward six standard deviations between the mean and the nearest specification limit) in any process – from manufacturing to transactional and from product to service. Six Sigma focuses on reducing process variation and enhancing process control, whereas lean drives out waste (non-value added processes and procedures) and promotes work standardization and flow. The distinction between Six Sigma and lean has blurred, with the term “lean Six Sigma” being used more and more often because process improvement requires aspects of both approaches to attain positive results.

Six Sigma is a method that provides organizations tools to improve the capability of their business processes. This increase in performance and decrease in process variation helps lead to defect reduction and improvement in profits, employee morale, and quality of products or services. “Six Sigma quality” is a term generally used to indicate a process is well controlled (within process limits ±3s from the center line in a control chart, and requirements/tolerance limits ±6s from the center line).

Implementation of Six Sigma

A typical Six Sigma project measures the current state and increases the performance of the business process to a new and statistically significant improved state using statistical tools. Standard Six Sigma capability refers to a very small number of possible failures that can exist outside the specification. The method most frequently associated with Six Sigma is DMAIC, which stands for Define, Measure, Analyze, Improve and Control. Before beginning any Six Sigma improvement project, it is necessary to select a process that, if improved, would result in reduced cost, superior quality or increased efficiency. The process also must possess measurable data because what you cannot measure you cannot improve. The process selected may currently be experiencing quality problems or generating a large amount of scrap.

The following is a list of the project phases, along with a brief description of each:


During the Define phase, the team should complete the following activities:

Develop a problem statement

The problem statement should contain a clear and concise description of the issue or issues that the project will address. In addition, the statement should include information concerning Critical to Customer Quality (CTQ) requirements (both internal and external), goals and benefits expected through completion of the project.

Define the Project Scope

The project scope sets the project boundaries. It is essential that the beginning and ending process steps are clearly identified and agreed upon prior to moving forward. Defining the scope will help keep the team focused on the issues at hand and tends to prevent or reduce “scope-creep”.

Identify Project Resources

Identify the champion, process owner and members of the team along with other resources that may be required on a part-time basis. Management must agree to support the project by committing the resources required for success.

Develop a Project Plan

The project plan should include a brief statement of how and when the project tasks are to be completed and by whom. In addition, designate the proper lines of communication and intervals of project status updates.

Develop a High Level Process Map

The high level map of the process is often developed in the SIPOC format which stands for Suppliers, Inputs, Process, Outputs and Customers. Upon completion of the high-level map, the team may select an area for development of a more detailed map.


During the Measure phase of the project, the team assembles a complete picture of the current state of the process and establishes a baseline through measurement of the existing system. Other activities may include:

Develop Detailed Process Maps

Develop detailed process maps for high-risk areas of the process, or areas where additional information is required. A detailed process map may reveal process inefficiencies such as long or incorrect cycle times, bottlenecks or non-value added process steps. The process map can also identify where data may be collected.

Develop Data Collection Plan

Define the methods and objectives of the data collection process. Identify what will be measured, the tools or equipment required, how to measure, how many and how often. In addition, determine the forms that will be used to document the data

Validate the Measurement System

A Measurement System Analysis (MSA) may be required to assure that the data collected is accurate. If your data is not accurate you could make decisions based on incorrect information. If Gage Repeatability & Reproducibility (GR&R) is greater than 30%, you may need to make improvements to the measurement system prior to proceeding with data collection.

Collect the Data

The emphasis during data collection should be gathering data that aids in further defining the problem. In addition, the data should provide information regarding possible causal factors that provide indications of how, when or where the problems occur. In many cases it will be necessary to gather data on process performance over a period of time. One of the key tools for collecting that data is the control chart. The control chart can help identify any trends or outlying measurements.


The focus of the Analyze phase is to identify all possible causal factors and determine the root cause of the problem.

Analyze the Data

The methods used to analyze the data depend on the type of data collected. The data can be analyzed graphically using scatterplots or frequency plots. Statistical analysis should also be performed. In most Six Sigma projects, an Analysis of Variance (ANOVA) is often performed. Other options include Correlation Analysis and Chi-Square testing.

Identify Causal Factors

This is accomplished using various tools and techniques. One widely used method for gathering and organizing possible causal factors is the Fishbone or Ishikawa diagram. The diagram is often used during brainstorming sessions. The diagram resembles the skeleton of a fish. The main branches of the diagram are usually labeled with the 6Ms: Man, Material, Method, Machine, Measurement and Mother Nature (Environment). The possible causal factors are then listed under each category. The top possible causes derived from the exercise are circled on the diagram and may then be investigated further.

Determine the Root Cause(s)

Often we identify possible causes and implement countermeasures and the problem goes away but eventually returns. This is because we have only treated a symptom of the problem and not the actual root cause. One popular and effective method for determining the root cause is 5 Why and 5 How. The 5-Why method is simply asking the question “Why” enough times until you get past all the symptoms of a problem and down to the root cause. The 5 How’s are used to determine a permanent solution to the root cause(s) of the problem.


At this point in the project, the team has identified possible root causes of the problem. The Improve phase should identify, implement and validate corrective actions to resolve any process issues and improve performance

Identify Potential Solutions

The team should identify possible process improvements that would increase process efficiency, improve quality and operator safety. Brainstorming is commonly used to generate a list of potential solutions. This can be done with a 5 How exercise or close examination of the process maps and statistical analysis results.

Analyze Failure Modes of Proposed Solution

Consider reviewing potential improvements for their risk and possible impact on other processes. A Failure Modes and Effects Analysis (FMEA) is often completed prior to implementation of any changes. The FMEA helps the team identify and address potential problems that may arise due to the improvements to the process. If an FMEA already exists for the current process, use it as a baseline and review for changes. The FMEA identifies potential risks along with their severity and likelihood of occurrence. The most critical issues are identified, allowing the team to develop a plan to minimize risk.

Validate Improvements

Prior to implementation, any process improvement should be validated using statistical methods. The team must verify that the improvement resolved the issue. Validation may be achieved through pilot builds, data collection and analysis and / or creation of a future state process map. The updated map can then be used by the team to perform a Gemba walk of the process and ensure the improvements are completed and implemented correctly.


The objective of the Control phase is to support and maintain the gains realized during the Improve phase. Proper action must be taken to assure the process does not regress back to its previous state. In order to achieve this goal the team will need to take the following steps:

Update Process Documentation

The team must ensure that all process documentation is updated with the changes to the process due to the improvements implemented. The documents that should be updated include Standard Work, Process Maps, Work Instructions, Control Plans, Visual Aids, etc.

Associate Training

Assure that all associates are trained on the process and understand the improvements that were introduced and how it affects their responsibilities. The associates should be informed of the purpose of the changes and the benefits of making these changes.

Implement Statistical Process Control (SPC)

SPC will monitor the performance of key steps in the process that relate to the CTQs identified during the Define phase. The control chart should be updated on a regular basis. The associates or process owner should review the charts for any evidence of shifts or trends in the process.

Create a Process Monitoring Plan

This is one key area where Six Sigma sets itself apart from basic project management The purpose of the monitoring plan is to document how the performance of the process will be monitored over time. The plan should include the metrics that will be monitored, the method of documentation, frequency of measurement and sample size. In addition, the plan should specify who will be notified if there is an issue, the method and timing of the communication, what response is required and who is responsible for executing the response.


The team should celebrate the successful completion of the project. Management should acknowledge the effort put forth in completing the project and the benefits realized from the project. Once the Control phase tasks have been completed, it’s time to transfer ownership of the new process to the original process owner. The team should discuss with the champion or Black Belt facilitator any opportunities to carry over the improvements made to other similar processes. Six Sigma and the DMAIC process work. Many organizations have realized enormous benefits over time. Be careful not to attempt to solve every problem right away, try not to go outside the boundaries of your project scope and do not skip any steps in the process. Trust the process and it will work for you.

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