Six-Sigma in Lean Construction Systems: Opportunities and Challenges

One of the tenants of lean construction states that achieving reliable workflow is possible when sources of variability are controlled. Under a lean paradigm, the effects of variability are buffered through excess inventory, flexible capacity, and/or work-ready backlogs. The common element between these three approaches to tackle production process variability is that they are all attempts to combat the effects of variability and not to reduce or eliminate variability altogether. Reducing or eliminating the variability that plague production processes requires the removal of the root causes of variability –a difficult but not impossible task. Six Sigma is a statistical-based methodology that provides a structured framework to organize and implement strategic process improvement initiatives to attain reductions in process variability. In this paper, the origin of Six Sigma is reviewed with a brief discussion of its methods and metrics. The application of the Six Sigma rolled throughput yield and sigma quality level metrics to the Last Planner System is demonstrated. Using the Lean Project Delivery System as a foundation, the paper suggests Six Sigma applications and research opportunities in Lean Construction.