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'''Control limits''' are horizontal lines drawn on an [[statistical process control|statistical process]] [[control chart]], usually at a distance of ±3 [[standard deviation]]s of the plotted [[statistic]] from the statistic's [[mean]].  
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'''Control limits''' are horizontal lines drawn on an statistical process control chart, usually at a distance of ±3 standard deviations of the plotted statistic from the statistic's mean.  


For [[normal distribution|normally distributed]] statistics, the area bracketed by the control limits will on average contain 99.73% of all the plot points on the chart, as long as the process is and remains in statistical control.
For normally distributed statistics, the area bracketed by the control limits will on average contain 99.73% of all the plot points on the chart, as long as the process is and remains in statistical control.


Control limits should not be confused with ''tolerance limits'', which are completely independent of the [[distribution]] of the plotted sample statistic.
Control limits should not be confused with ''tolerance limits'', which are completely independent of the distribution of the plotted sample statistic.


==See also==
==See also==
*[[Statistical charts and diagrams]]
* [[Management]]
*[[Management]]
*[[Measurement]]
*[[Quality]]
*[[Quality control]]
*[[Evaluation methods]]
*[[Process management]]


[[Category:Statistics]]
[[Category:Statistics]]

Latest revision as of 16:15, 7 June 2009

Control limits are horizontal lines drawn on an statistical process control chart, usually at a distance of ±3 standard deviations of the plotted statistic from the statistic's mean.

For normally distributed statistics, the area bracketed by the control limits will on average contain 99.73% of all the plot points on the chart, as long as the process is and remains in statistical control.

Control limits should not be confused with tolerance limits, which are completely independent of the distribution of the plotted sample statistic.

See also