Six Sigma


First, What is Six Sigma?

First, what it is not. It is not a secret society, a slogan or a cliche. Six Sigma is a highly disciplined process that helps us focus on developing and delivering near-perfect products and services.

For a normally distributed data set, the empirical rule states that 68% of the data elements are within one

standard deviation of the mean, 95% are within two standard deviations, and 99.7% are within three standard

deviations. Graphically, this corresponds to the area under the curve as shown below for 1 and 2 standard

deviations. The empirical rule is often stated simply as 68-95-99.7. Note how this ties in with the range rule of

thumb, by stating that 95% of the data usually falls within two standard deviations of the mean.

[+/- 1 std shaded under normal curve]

Data within 1

[+/- 2 std shaded under normal curve]

(left) and 2


Sigma is a symbol meaning how much deviation exists in a set of data. It is sometimes called a “bell curve.” In statistics, this is called a standard normal distribution, but the idea is the same. In a bell curve, 50% of the values lie above the mean (average) and 50% of the values lie below the mean. In Statistics we take it a step further and delineate certain data points within that timeline

The sigma value is measured against this. The further out from the mean on the time line the greater the sigma. The objective is to get the minimum sigma. To reduce the variance as much as possible.

The 6 Sigma Proposition

All to often businesses base their performance on an average and average-based measures of the recent past. However, customers don’t judge businesses on averages; they feel the variance in each and every transaction. Customers value consistent, predictable business processes and products that deliver world-class levels of quality. Six Sigma focuses first on reducing variation and then on improving process capability

A common goal with a Six Sigma program is to minimize variation within all of our critical processes. Examples of key processes include: Invoicing/Billing customers; New product development; Processing customer orders; Managing human resources (including payroll, holiday applications, etc.); Hiring employees; Budgeting; Paying bills;Evaluating vendors.

Quantitatively, this means working towards Six Sigma quality, or fewer than 3.4 defects per million “opportunities.” An opportunity is defined as a “chance for non-conformance” (or put another way not meeting required specifications). So the business must adjust it’s culture towards accepting a near perfect operation in executing key processes. Such a cultural change will directly contribute towards customer satisfaction and increased productivity.

Six Sigma Definition

Six Sigma stands for Six Standard Deviations (Sigma is the Greek letter used to represent standard

deviation in statistics) from mean. Six Sigma methodology provides the techniques and tools to improve

the capability and reduce the defects in any process. It allows for only 3.4 defects per million

opportunities for each product or service transaction. Six Sigma relies heavily on statistical techniques to

reduce defects and measure quality.

The central idea behind Six Sigma is that if you can measure how many "defects" you have in a process, you can

systematically figure out how to eliminate them and get as close to "zero defects" as possible. To achieve Six

Sigma Quality, a process must produce no more than 3.4 defects per million opportunities. An "opportunity" is

defined as a chance for nonconformance, or not meeting the required specifications. This means we need to be

nearly flawless in executing our key processes.

Key Concepts of Six Sigma

At its core, Six Sigma revolves around a few key concepts.

Six Sigma Glossary

Quality Approaches and Models

DFSS (Design for Six Sigma) - A systematic methodology utilizing tools, training and measurements to enable us to design products and processes that meet customer expectations and can be produced at Six Sigma Quality levels.

DMAIC (Define, Measure, Analyze, Improve and Control) - A process for continued improvement. It is systematic, scientific and fact based. This closed-loop process eliminates unproductive steps, often focuses on new measurements, and applies technology for improvement.

Six Sigma - A vision of quality, which equates with only 3.4 defects per million opportunities for each product or service transaction. Strives for perfection.

Quality Tools

Associates are exposed to various tools and terms related to quality. Below are just a few of them.

Control Chart - Monitors variance in a process over time and alerts the business to unexpected variance which may cause defects.

Defect Measurement - Accounting for the number or frequency of defects that cause lapses in product or service quality.

Pareto Diagram - Focuses our efforts on the problems that have the greatest potential for improvement by showing relative frequency and/or size in a descending bar graph. Based on the proven Pareto principle: 20% of the sources cause 80% of any problems.

Process Mapping - Illustrated description of how things get done, which enables participants to visualize an entire process and identify areas of strength and weaknesses. It helps reduce cycle time and defects while recognizing the value of individual contributions.

Root Cause Analysis - Study of original reason for nonconformance with a process. When the root cause is removed or corrected, the nonconformance will be eliminated.

Statistical Process Control - The application of statistical methods to analyze data, study and monitor process capability and performance.

Tree Diagram - Graphically shows any broad goal broken into different levels of detailed actions. It encourages team members to expand their thinking when creating solutions.

Quality Terms

Black Belt - Leaders of teams responsible for measuring, analyzing, improving and controlling key processes that influence customer satisfaction and/or productivity growth. Black Belts are full-time positions.

Control - The state of stability, normal variation and predictability. Process of regulating and guiding operations and processes using quantitative data.

CTQ: Critical to Quality (Critical "Y") - Element of a process or practice which has a direct impact on its perceived quality.

Customer Needs, Expectations - Needs, as defined by customers, which meet their basic requirements and standards.

Defects - Sources of customer irritation. Defects are costly to both customers and to manufacturers or service providers. Eliminating defects provides cost benefits.

Green Belt - Similar to Black Belt but not a full-time position.

Master Black Belt - First and foremost teachers. They also review and mentor Black Belts. Selection criteria for Master Black Belts are quantitative skills and the ability to teach and mentor. Master Black Belts are full-time positions.

Variance - A change in a process or business practice that may alter its expected outcome.