Six Sigma is a disciplined method that works in phases. A Six Sigma Black Belt (BB) learns that he/she must complete a phase before going to the next. The phases in order are: Define, Measure, Analyze, Improve, and Control (also known as DMAIC). To ensure that a BB does not go from one phase to the next prematurely, checkpoints (tollgates) are set up. These tollgates might be a number of questions (checklist items) that the Master Black Belt (MBB) or Champion goes through with the BB to ensure satisfaction with the phase. Once completed, the BB can move to the next phase.
After leading and coaching many Six Sigma projects, I found it more natural to go back and fourth between phases. For example, I found myself making a number of iterations among phases (Measure==>Analyze==>Improve==>Measure… and so on). Once the process is improved and measured to meet established goals, it can then move to the Control phase. Feedback to the Define should be open after evaluating process control.
In addition to measuring improvements using appropriate metrics, the real test of success is sustaining such improvements over time.
What is your experience?