Both Lean and Six Sigma focus on eliminating waste and providing the best possible quality to products and services at lowest cost. The scope of these two methods however differs.
Lean is a continuous and on going activity that strives to change the culture of the organization and ingrain among the workforce the habit of relentlessly seeking out and removing waste across-the-board. The Lean culture reduces cycle times and streamlines processes, resulting in improved service levels, better productivity, optimal asset utilization, increased cash flow, right-sized inventory levels, shorter changeover times, better product designs, and reduced input costs. Lean however does little to improve actual process capabilities.
Six Sigma is a project-based methodology that aims to improve customer satisfaction by focusing on elimination of variation in a specific process. Six Sigma does not consider whether the process itself is per se a waste or not, and does little to optimize the process flow either. The impact of Six Sigma naturally remains confined to whatever the scope of the Six Sigma project.
The focus of Lean Six Sigma is to leverage the power of Lean and Six Sigma and improve productivity through quality improvements that eliminate variation, and through process re-design that reduce lead times, eliminate waste, and re-look inventory levels, all using analytical tools.
Lean Six Sigma also aims at empowering the workforce to manage change by involving them in the change management activity under the guidance of trained mentors. Traditional Six Sigma implementation team remains a closed group of green belts under the leadership of a black belt. Lean Six Sigma requires such a team, but also requires such team members to remain competent in Lean tools and also involve the entire workforce in the change management process. Again, Lean Six Sigma provides a definite quantitive and statistical basis for the implenentaion of hitherto pure Lean concepts.