It looks like I’m entering this thread late, to say the least. But here’s how I see it. There have been three HUGE initiatives in the past 30 years or so: quality/TQM, Six Sigma, and Lean. All three started long before they became popular (Post WWII.) I believe all are related and fall under the umbrella of systems and industrial engineering.
As I see it, the essence of each approach is as follows:
QUALITY is doing the right things right. This means that (1) you’ve identified what the right things are, perhaps by studying the VOC, and (2) you have systems in place to assure that they are done right and to take appropriate action when they are not. Quality implies that you’re not doing the wrong things, i.e., things that the customer does not want.
Six Sigma focuses on modeling complex business processes and using the models to improve performance rapidly. A model is an explicit, logical linkage of outcomes to root causes. Many, but not all, Six Sigma models are mathematical. If the linkage between causes and outcomes is already known, there is no need for Six Sigma. As always, all models are wrong, but some models are useful. Six Sigma goes somewhat beyond SIE because using the models to improve requires a significant management component. Since many of the improvements involve customers, Six Sigma and Quality are linked.
Lean systematically identifies and eliminates waste in value streams. This requires that you know what the organization’s value streams are and can identify waste defined as non-value added activities. Since value is defined by customers, Lean is linked to Quality. In many cases Lean can be applied without Six Sigma because the linkage between the waste and its causes is well understood. However, when the root cause of waste isn’t known, Six Sigma provides important tools and techniques for modeling it. Thus, Lean is linked to Six Sigma as well.
In summary:
Quality is working better.
Lean is working efficiently.
Six Sigma is working smarter.
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