- Six Sigma focuses upon process capability and reduction of DMPO,
- Lean focuses on the elimination of waste in a value stream.
- Six Sigma is about improving Quality.
- Lean philosophy is about improving Efficiency.
The two bodies of knowledge meld together well, although it took some time for the naysayers to agree. When you're looking at almost any improvement project, it just makes common sense to applies both methodologies. Certainly increasing your process capability by eliminating the possibility of errors is a wonderful goal, but by also removing the non-value added activities, and streamlining the process for additional efficiency.
it's like two improvements for the price of one! One should look at both methods when implementing an improvement project.