See DoD Directive 5010.42, 15 May 2008
Slow, wasteful business processes are the problem and little or no historical process data;
Goal: Process speed
Focus: Lean
Streamlined, highly efficient business processes, but process variation identified a problem based on statistically-significant historical data;
Goal: Process consistency
Focus: Six Sigma
Slow, wasteful business processes combined with low performance or quality variation;
Goal: Speed and consistency
Focus: integrated Lean and Six Sigma