For more on six-sigma control, see six sigma. These rules are discussed in greater detail later in this section.Ĭontrol Charts are commonly used in six sigma control today, as a means of overall process improvement.
In generalized terms, if data points fall within three standard deviations of the mean (within the red lines), the process is considered to be in control. The centerline is the mean value of the data set and the green, blue and red lines represent one, two, and three standard deviations from the mean value.
XBAR IN STATS PDF
The image below shows the control chart for a data set with the PDF overlay. For example, if an engineer knows the mean (grand average) value, standard deviation, and range of a process, this information can be displayed as a bell curve, or population density function (PDF). Control charts build on this basic idea of statistical analysis by plotting the mean or range of subsequent data against time. For good and safe control, subsequent data collected should fall within three standard deviations of the mean. Then, subsequent data can be compared to this already calculated mean, standard deviation and range to determine whether the new data fall within acceptable bounds. The boundaries for these classifications are set by calculating the mean, standard deviation, and range of a set of process data collected when the process is under stable operation. \)Ī process may either be classified as in control or out of control.
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