Nelson’s rules are a set of rules that are used in control charts to determine when a process is unstable and needs to be adjusted. Control charts are frequently used in Lean Six Sigma process improvement projects to monitor process performance and identify deviations from normal conditions.
Nelson’s rules are applied to a process to identify “special cause” variation. Special cause variation is a variation that occurs outside of a process’s normal range of variation and is frequently caused by an assignable cause, such as a machine malfunction or a shift in the process mean.
The following are the rules:
- If one point is outside the control limits, investigate.
- If two of three consecutive points are on the same side of the centerline, investigate.
- If four consecutive points are increasing or decreasing, investigate.
- If eight consecutive points are on one side of the centerline, investigate
Nelson’s rules can help identify process instability in Lean Six Sigma process improvement projects, which can then be addressed through process improvement initiatives. Control charts and Nelson’s rules, for example, can be used in a product management organization to monitor the performance of product assembly processes, identify when a process is unstable, and address process instability through process improvement initiatives.
According to a critical review of the literature, Nelson’s rules are a valuable tool in Lean Six Sigma process improvement projects. Nelson’s rules assist Lean Six Sigma practitioners in quickly identifying when a process may require adjustment by providing a set of guidelines for identifying process instability. This can lead to better process performance, increased efficiency, and less waste.
Finally, Nelson’s rules are an important tool in Lean Six Sigma process improvement projects. Nelson’s rules provide a set of guidelines for identifying process instability and addressing process instability through process improvement initiatives, whether you are a Lean Six Sigma practitioner, a product manager, or simply interested in process improvement. Organizations can improve process performance, efficiency, and waste reduction by leveraging the power of control charts and Nelson’s rules.
