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|Table of Contents Statistical Tests Control Charts p- and c-Charts|
|See also: Control Charts, x- and R-Charts|
In order to monitor proportions of a process, such as the proportion of defect products in a production line, we can use either p-charts or c-charts.
The control limits are usually set by the following equations:
with being the mean of n proportions considered. Note that the band of tolerance is given by +/- 3 standard deviations of the distribution of proportions (binomial distribution).
A c-chart is quite similar to the p-chart, except that in this case the special outcomes (like defects) of a process are counted. The control limits are given by
again forming a band of +/- 3 standard deviations of an assumed Poisson
Last Update: 2006-Jšn-17