Lean Six Sigma is a business improvement methodology which combines tools from both Lean and Six Sigma. Traditionally, Lean focuses on speed, through the elimination of unnecessary process elements, and Six Sigma focuses on quality, through the pursuit of process control.
However, Lean alone can’t typically achieve process control, and Six Sigma alone can’t significantly reduce lead times. Whenever “Quality only” Six Sigma is applied to reducing variation in a single process step or to processes which are not value-added to the customer one runs the risk of “sub-optimizing the total” in order to “optimize the local.”
Conversely, whenever a value stream is mapped according to traditional Lean/Just-in-Time practices – especially in service organizations – the lead-time (or work-in-process) estimates do not typically incorporate the natural variation that can occur throughout a period of time, i.e., they do not reflect the range of values that would be characterized by collecting a representative sample of value stream maps. This could in turn, lead to the under – or over – estimation of certain inefficiencies.
Ultimately, by combining Lean and Six Sigma, the result is better quality and reduced lead times. System effectiveness integrates with the control of critical points in the value chain.