I open this question up for discussion – please add your comments. If I had to choose between a 4 sigma process and solid control plan versus a six sigma process and a weak or non-existent control plan, I’d take the first option. Unless the process is completely automated and free from any physical deterioration (as in the IT world), it is likely to deteriorate over time. A control plan, if implemented correctly, will protect the customer long after the Six Sigma team has moved on to other projects. What are your experiences in this area?