2.2. Six Sigma
Some common perceptions and definitions of Six Sigma include:
A management philosophy.
Marketing hype.
A way to transform a company.
A way to create processes with no more than 3.4 defects per million opportunities.
Solving problems using data.
A way to use training credits.
Something a company has to do before Lean.
Making improvements using data.
A way to make money from consulting, training, and certification.
A pseudo-religion.
A way to get your next job.
Something a company does after Lean.
In spite of this diversity, there seems to be broad agreement that a Six Sigma initiative involves a variety of stakeholders and is a project-based method utilizing cross-functional teams. A performance gap is the only legitimate reason for spending the time and resources needed to execute a Six Sigma project. From this point of view, questions such as the following are vital to a Six Sigma deployment:
How big should the performance gap be to make a project worth doing?
How can you verify that a project did indeed have the expected impact?
However, for reasons of space, our brief discussion will address only the steps that are followed in a typical Six Sigma project once it has gained approval, and what resources are needed to execute it.
Using the background presented in the beginning of this chapter, we offer our own succinct definition of Six Sigma:
Six Sigma is the management of sources of variation in relation to performance requirements.
Here, management refers to some appropriate modeling activity fed by data. Depending on both the business objectives and the current level of understanding, management of sources of variation can mean:
Identifying and quantifying sources of variation.
Controlling sources of variation.
Reducing sources of variation.
Anticipating sources of variation.
A Six Sigma deployment effort typically starts with the following infrastructure:
A senior executive, often a president or chief executive officer, provides the necessary impetus and alignment by assuming a leadership role.
An executive committee, working operationally at a level similar to that of the senior executive, oversees the Six Sigma deployment.
A champion sponsors and orchestrates an individual project. This individual is usually a member of the executive committee and has enough influence to remove obstacles or allocate resources without having to appeal to a more senior individual.
A process owner has the authority and responsibility to make improvements to operations.
A black belt supports project teams, taking a leadership role in this effort. This individual is a full-time change agent who is allocated to several projects. A black belt is usually a quality professional, but is often not an expert on the operational processes within the scope of the project.
A green belt works part-time on a project or perhaps leads a smaller-scope project.
A master black belt mentors the Six Sigma community (black belts and green belts), often provides training, and advises the executive committee. A master black belt must have a proven track record of effecting change and be a known and trusted figure. This track record is established by having successfully completed and led numerous Six Sigma projects, ideally within the same organization.
To guide Six Sigma projects that seek to deliver bottom-line results in the short or medium term, black belts typically use the Define, Measure, Analyze, Improve, and Control (DMAIC) structure, where DMAIC is an acronym for the five phases involved:
Define. Define the problem or opportunity that the project seeks to address, along with the costs, benefits, and the customer impact. Define the team, the specific project goals, the project timeline, and the process to be improved.
Measure. Construct or verify the operational definitions of the Ys, also called critical to quality (CTQ) metrics and measures. Plot a baseline showing the level and current variation of the Ys. Quantify how much variation there is in the measurement process itself, in order to adjust the observed variation in the Ys and to improve the measurement process, if needed. Brainstorm or otherwise identify as many Xs as possible, in order to include the Xs that represent root causes.
Analyze. Use process knowledge and data to determine which Xs represent root causes of variation in the Ys.
Improve. Find the settings for Xs that deliver the best possible values for the Ys, develop a plan to implement process changes, pilot the process changes to verify improvement in the Ys, and institutionalize the changes.
Control. Lock in the performance gains from the Improve phase.
Depending on the state of the process, product, or service addressed by the project, a different set of steps is sometimes used. For instance, for products or processes that are being designed or redesigned, the Define, Measure, Analyze, Design, Verify (DMADV) or the Identify, Design, Optimize, Validate (IDOV) framework is often used. These structures form the basis of Design for Six Sigma (DFSS).[] Briefly, the phases of the DMADV approach consist of the following:
Define. Similar to the Define phase of DMAIC.
Measure. Determine internal and external customer requirements, measure baseline performance against these requirements, and benchmark against competitors and industry standards.
Analyze. Explore product and process design options for satisfying customer requirements, evaluate these options, and select the best design(s).
Design. Create detailed designs of the product and process, pilot these, and evaluate the ability to meet customer requirements.
Verify. Verify that the performance of the product and process meets customer requirements.
This brings us back full circle to our own definition: Six Sigma is the management of sources of variation in relation to performance requirements. With a little thought, perhaps you can see how large parts of DMAIC, DMADV, or IDOV involve different ways to manage variation. For example, a DFSS project would involve techniques and tools to "anticipate sources of variation" in the product, process, or service.