What is Six Sigma?

Six Sigma is a powerful problem solving toolkit that is used for both manufacturing and transactional processes.

While the statistical definition of Six Sigma is far less important than the improvement methodology itself, the illustrations below provide a solid background on where the Six Sigma term comes from.  Also in this article you will find practical advice on implementing Six Sigma.

For those unfamiliar with histograms and the normal distribution model, read histograms and normal probability curve before reading the next section, and don’t let the statistics deter you – Six Sigma is much more about process improvement less about theoretical defect rates.

Statistical Definition

Six Sigma uses the normal distribution equation (the “bell curve” distribution that fits a number of real-world situations) , which predicts 3.4 defects-per-million over the long run for processes that have at least six standard deviations between the process average and the nearest specification limit (see image below).

The important point is that a Six Sigma process has extra “cushion” between the outer extremes of the process results and the specification limits, so the process can drift over time without creating defects:

the statistical definition of Six Sigma


Short Term Versus Long TermVariation

The Six Sigma philosophy assumes that the process average will drift over time, and that the variation observed in a snapshot (sample) of data will deteriorate somewhat over the long run.  The process drift is assumed to be a maximum of 1.5 standard deviations , and the 3.4 DPM level takes this theoretical “mean shift” into account.  It is unlikely that any given process drifts by exactly 1.5 standard deviations over the long run – some processes may not drift at all, and some may drift more than 1.5 standard deviations – but the assumption of a 1.5 sigma mean-shift is better than ignoring mean shift as a factor in long term variation.
process mean shift - short term versus long term data

Game Changing Process Improvement

While books have been written explaining the theory behind Six Sigma’s probability model, the real power of Six Sigma lies in the DMAIC process.  DMAIC is a collection of quality improvement tools that are combined into a 5-step approach:  Define -> Measure -> Analyze -> Improve -> Control.  When these tools are combined with the intent of achieving Six-Sigma process capability, then a robust, defect-free process is a realistic expectation.


Six Sigma implementation is effective when the DMAIC Process is implemented inside an existing framework for continuous improvement.  This framework is often referred to as Operational Excellence (OPEX), and consists of the following major elements –

  • The organization has defined Key Performance Indicators (KPI’s) that represent the most important measures for success.  Successful teams understand that identifying a select-few metrics and focusing on them consistently will result in a long-term competitive advantage.  Other metrics will be collected and monitored as they are in most organizations, but the KPI’s will get most of the focus.
  • Teams throughout the organization understand the top-level KPI’s and know how their work activities affect those KPI’s. For example, a customer call center understands that hiring standards, ongoing training, and call monitoring will have a big impact on an overall Customer Satisfaction KPI.  The call center will have its own  metrics that focus on these areas.
  • KPI’s are grouped into dashboards that are always in front of the management team.
  • Structured KPI reviews take place at regular intervals.  The management team creates a structure for these reviews and demonstrates strong discipline in making the reviews happen.  The types and locations of reviews can vary depending on which teams in the organization have the greatest impact on a given KPI at a given point in time.  A number of companies will conduct daily management walks that stop at metric boards, which are then reviewed with the team leaders in key areas.  Other reviews might be held monthly in a conference room or video conference call to focus on top-level KPI’s with their respective owners.

Once an OPEX or goal deployment process is in place, the following approach is recommended for bringing Six Sigma into the organization –

Identify Opportunity Areas

This is a precursor to finding Black Belt candidates for certification.  While a Black Belt need not be a technical expert in the process areas that require the most focus, they should be familiar enough with the process (whatever process is going to be improved) to work effectively as a team leader.

Identify and Train Process Improvement Leaders

This is one of the most important steps in the process.  Every organization is different, but we recommend the following  guidelines when selecting a person to be a Six Sigma implementation leader –

  • Go with an in-house person if possible, someone who is competent (or at least able to converse intelligently with process leaders) in the key process areas that need focus.
  • The individual should be respected across the organization (especially by the leadership team – he/she will need their support) and should be a proven project leader.
  • The individual should have a passion for problem solving, and should be very interested in learning more about the DMAIC process.

We recommend Six Sigma training through a formal program that includes project work and extensive interaction with an experienced training team.  Depending on the size of your organization, you may choose to put more than one person through this first round of training and certification. 

Develop Early Success

Using the define stage thought process, identify one or two projects that the Black Belt(s) in-training can lead while going through the certification process.  Reputable certification programs require that trainees implement projects in parallel with training, and successfully apply the DMAIC toolkit to achieve results.

Train the Management Team and Functional Leaders

It’s very important that the management team understand the DMAIC process so they can support the implementation.  At a minimum, the newly certified Black Belt(s) should put together a ½ day overview outlining the DMAIC process.

Train the Remainder of the Organization in Basic DMAIC

Train the remainder of the organization (at a minimum, those who participate in the OPEX process) in the basic DMAIC tools.  This is commonly referred to as Yellow Belt training.

Implement a DMAIC Report-Out

Instead of simply reporting metrics and countermeasures, teams should now present a standard DMAIC 4-Block that shows the KPI trend, pareto chart, causes identified, and planned/implemented corrective actions.  It will be the management team’s responsibility to identify problems or opportunities that require Black Belt projects.

The above elements should get any organization off to a good start with Six Sigma.  The chart below shows typical resource deployment for driving continuous improvement.  Keep in mind that Black Belts and Master Black Belts not only drive specific projects, but also spend time coaching teams working inside the OPEX process – this approach provides maximum leverage across the organization.


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