There has been a flurry of activity in the last year trying to integrate the concepts of Six Sigma and Lean. A lot of it is driven by consultants looking for the next new thing and quick buck... and some have even trademarked variations of the words Lean, Six, and Sigma.
But are the two concepts really compatible?
Toyota is the master of Lean, and focuses on stripping waste out of every possible business process, but does not embrace Six Sigma. GE has made Six Sigma, and expensive green and black belt training programs, a must-have at many major corporations. There are also examples on both sides of companies that implement the concept but still struggle... such as Motorola and its Six Sigma prowess.
Six Sigma optimizes every possible process to reduce potential failure rates. This can create massive statistical exercises with results understandable to only a few people, and perhaps "analysis paralysis". There is no doubt that it can improve quality... eventually. Lean reduces the waste in all possible processes, but does not necessarily optimize. The difference in character between companies that embrace these different concepts can be stunning... and sometimes difficult to manage as we've mentioned before.
One specific circumstance to avoid: using Six Sigma to optimize a process that Lean will determine to be a waste. However the two concepts can be used together, as long as you recognize their specific purpose,design, and potential conflicts. The Wall Street Journal had a recent article entitled "Rethinking Quality Improvement" that questioned the impact of Six Sigma on innovation. The iSixSigma blog has some balancing thoughts.
Before embarking on a Six Sigma statistical optimization of a process, use Lean to ensure that process is not waste to begin with.