Special Cause Variation: Difference between revisions
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# Control any damage or problems with an immediate, short-term fix. Be careful not to view this fix as a permanent solution. |
# Control any damage or problems with an immediate, short-term fix. Be careful not to view this fix as a permanent solution. |
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# Once a quick fix is in place, search for the root cause by asking [[5 Whys]] which is one of the techniques in [[Six Sigma]] technology. |
# Once a quick fix is in place, search for the root cause by asking [[5 Whys]] which is one of the techniques in [[Six Sigma]] technology. |
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# If one of the answers gernerated from [[5 Whys]] is "don't know", then Cause-and-Effect diagram ([[Ishikawa diagram]]) may be |
# If one of the answers gernerated from [[5 Whys]] is "don't know", then Cause-and-Effect diagram ([[Ishikawa diagram]]) may be employed. Other methodologies which are used for seeking root cause include: |
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* [[Kepner and Tregoe method]] |
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# Once the root cause is discovered, develop a longer-term remedy. Most special causes have a negative impact on the output of the process and need to be removed. Occasionally, a special cause can have a positive impact depending on the nature of the process. If this is the case, finds ways to capture and integrate it into the system. |
# Once the root cause is discovered, develop a longer-term remedy. Most special causes have a negative impact on the output of the process and need to be removed. Occasionally, a special cause can have a positive impact depending on the nature of the process. If this is the case, finds ways to capture and integrate it into the system. |
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Revision as of 05:54, 10 November 2006
Special Cause Variation, also known as assignable cause variation, is the fluctuation that is caused by known but unpredictable factors, resuling in a non-random distribution (Normal Distribution) of output data [1]. It will usually show up in a Control chart as outlier samples (i.e., exceeding the lower or upper control limit) or as a systematic pattern (run) of adjacent samples. It will also affect the calculation of the chart specifications (center line and control limits). Unlike Common Cause Variation, special causes of variation can be eliminated by reacting to individual variations.
How to Respond
It is not difficult to deal with special causes if they are spotted early. Tracking down special causes relies heavily on people's memories of what made that occurrence different from all the others. People may quickly forget any unusual circumstances that may have triggered the unusual variation.
When a special cause is spotted, do the following step by step:
- Control any damage or problems with an immediate, short-term fix. Be careful not to view this fix as a permanent solution.
- Once a quick fix is in place, search for the root cause by asking 5 Whys which is one of the techniques in Six Sigma technology.
- If one of the answers gernerated from 5 Whys is "don't know", then Cause-and-Effect diagram (Ishikawa diagram) may be employed. Other methodologies which are used for seeking root cause include:
- Once the root cause is discovered, develop a longer-term remedy. Most special causes have a negative impact on the output of the process and need to be removed. Occasionally, a special cause can have a positive impact depending on the nature of the process. If this is the case, finds ways to capture and integrate it into the system.
How to Avoid
Spcial Cause Variation can be avoided by
- Changing the process to accommodate the special cause. This usually adds cost and bureaucracy.
- Blaming individuals soly. Not only does everyone makes mistakes, but also chances are that the problem would have occurred regardless of individuals involved.
- Exhorting workers to simply "do better." Most people, excetp for elites, can only do as well as the system allows them to do.