Variation Reduction vs Mean Improvement

[Vishwadeep Khatri 265]

Q 219. Six Sigma helps us improve the process either by reducing the variation and/or improving the mean. Is it mandatory to first reduce variation and then improve the mean? Support your answers with examples

 

 

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[Vishwadeep Khatri 265]

Whether we want to improve mean or reduce variation first is entirely dependent on the expectations from process, the current situation and the cost-benefit analysis. Let us see some scenarios - 

 

• If specification limits are one sided and shift in mean is easier and cheaper, it makes sense to shift mean. 
• If specification width (tolerance) is small, it will make sense to reduce variation first as just the shift of mean will not provide a consistent outcome over time. 
• If specification width (tolerance) is large, shifting mean (if feasible and low cost) may be sufficient and reducing varion may not be needed.