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The Six Sigma methodology seeks to reduce and ultimately eliminate variation within a process. It applies a five-phase project management approach and uses the standard deviation (sigma) as the controlling attribute for the process.

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Quick reference

Six Sigma Principles

The Six Sigma methodology seeks to reduce and ultimately eliminate variation within a process. It applies a five-phase project management approach and uses the standard deviation (sigma) as the controlling attribute for the process.

When to use

The Six Sigma methodology is both a principle-based and a tool-based methodology. The principles should guide the project team through the process and assist with the selection of tools.

Instructions

The Six Sigma methodology has several key principles that are embodied within it. These principles were tested and proven at Motorola on the manufacturing product lines.

The measures of Defects per Million Opportunities (DPMO) and process sigma are used to measure the level of variation and out-of-specification conditions of the result from the business process. Variation is the enemy of process control and the Six Sigma analysis first measures this variation and then strives to reduce or eliminate the sources of variation. This is the overarching goal and organizing principle of the Six Sigma methodology.

Another key principle is that of an orderly and structured problem solving process that is based upon the analysis of data. The five phases of Define, Measure, Analyze, Improve and Control guide the team though this approach.

The first two phases, Define and Measure, are used to articulate the real problem. The first phase determines the problem from a business and customer perspective. The second phase then collects data about the product or process in order to determine what is actually happening and where the problem really occurs. The third phase is the statistical analysis of the problem. Data is used to statistically validate the real problem that is causing the variation and out-of-specification conditions. The final two phases are associated with the problem solution. The Improve phase designs the solution and validates that it is effective. The Control phase implements that solution and changes all associated processes, procedures, and systems that must change to ensure the improvement becomes the new standard operation.

Six Sigma strives to create processes where the normal variation is much less than the allowed variation based upon the process specification limits. Understanding the sources and magnitude of variation are essential elements of the Six Sigma methodology.

Hints & tips

  • The DMAIC process guides the team through the analysis and ensures they don’t jump to the wrong conclusion.
  • Variation is the enemy of process control. Stay focused on sources of variation and don’t get lost in the statistical analysis.
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  • 00:05 Hi, this is Ray Sheen.
  • 00:06 The Six Sigma methodology has as its foundation some key principles,
  • 00:11 let's take a look at those principles.
  • 00:14 In order to better understand the Six Sigma principles,
  • 00:17 let's start with a quick review of the background of Six Sigma.
  • 00:21 It was developed at Motorola for
  • 00:23 the purpose of improving the quality of manufactured products.
  • 00:27 So it wasn't esoteric and philosophical, it was very practical and
  • 00:31 implemented in the manufacturing shop.
  • 00:34 This methodology relies on the elimination of variation in the process inputs and
  • 00:39 outputs.
  • 00:40 When variation occurs, the process must add steps to measure whether the variation
  • 00:44 is beyond the allowable performance limits.
  • 00:47 Now this adds inspection costs.
  • 00:48 Now when the variation is too large, the business must scrap or
  • 00:52 re-work the product, which adds additional costs and delays in production.
  • 00:57 Variation is the enemy of smooth, low-cost manufacturing processes.
  • 01:03 Six Sigma uses several measurements to monitor variation.
  • 01:07 One that has become very well known is defects per million opportunities,
  • 01:12 or DPMO, sending the message that any defect is a problem.
  • 01:16 That measure, and the process standard deviation,
  • 01:20 can be translated into a process sigma, which is a way of measuring the level of
  • 01:24 uncertainty in any process input or output.
  • 01:27 The Six Sigma methodology has a structured process for how the analysis is conducted.
  • 01:34 The five phases, define, measure, analyze, improve, and control,
  • 01:39 guide the team through the problem solving, and problem solution process.
  • 01:44 In fact, those five steps are so
  • 01:46 important in the methodology that I wanna spend a little more time on them.
  • 01:51 The DMAIC process, which again, stands for define, measure, analyze,
  • 01:57 improve and control, provides the logical process for Six Sigma teams to follow.
  • 02:03 The first two phases create the problem definition.
  • 02:06 The define phase identifies the problem from the business standpoint and
  • 02:10 sets the boundaries of the project.
  • 02:12 The measure phase digs into the process and
  • 02:15 data to find the real problem and specify the magnitude of that problem.
  • 02:21 Six Sigma has a reputation for going overboard on statistical analysis.
  • 02:26 If that happens, it's during the analyze phase.
  • 02:30 A key principle in this phase is that the analysis of the problem must be based on
  • 02:34 statistically demonstrated facts.
  • 02:37 It isn't enough to think you know the reason for the problem, you must be able
  • 02:41 to demonstrate with statistical data that you have the root cause or causes.
  • 02:47 There is a structured approach for how you work through this phase.
  • 02:51 The final two phases, improve and control, are now focused on the problem solution.
  • 02:56 The first of these phases, improve, is the design and validation of the solution.
  • 03:02 And the final phase, control, is the implementation of that solution.
  • 03:06 Things don't get better just because someone wrote a memo or did a study.
  • 03:11 The process and procedure must be changed, people trained, and
  • 03:15 the ongoing control plan put in place, to make sure the improvement sticks.
  • 03:21 Let me finish this session with a discussion about Sigma.
  • 03:25 Sigma takes the name from the Greek letter that is used to represent the standard
  • 03:30 deviation, a statistical measure of the spread within a set of data.
  • 03:35 The term Process Sigma refers to the ability of that process to consistently
  • 03:40 provide results that are within the allowable limits of the process.
  • 03:45 As I already mentioned, every process parameter has some inherent variability.
  • 03:49 When that variability is due to random causes, the bell-shaped curve is a good
  • 03:54 representation of the level of variability.
  • 03:56 That means the variation is mostly in the center of the curve, but
  • 04:00 occasionally things are higher or lower than normal.
  • 04:03 In this picture, you see two lines.
  • 04:06 Consider these to be the allowed process performance specification limits.
  • 04:10 The first bell-shaped curve represents a two sigma process,
  • 04:14 and you can see that the curve stretches beyond these specification lines.
  • 04:19 That means that there will be some instances
  • 04:22 in the process output being out of specification.
  • 04:25 As you progress up the series of bell-shaped curves,
  • 04:28 we finally get to Six Sigma.
  • 04:31 In this case, the curve easily fits between the customer specification lines.
  • 04:36 When a process is operating at the Six Sigma level,
  • 04:40 the process should virtually never create an output that is out of specification.
  • 04:45 The process sigma then is a way for process managers and business managers to
  • 04:50 manage the quality of business processes and predict performance.
  • 04:54 Again, the key is to eliminate the variability and get the width of that bell
  • 04:59 curve of data to be much smaller than the allowable specification limits.
  • 05:07 These fundamental principles of a structured methodology,
  • 05:11 statistical analysis, and the removal of variation are at the heart of Six Sigma.

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