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The CUSUM Procedure


The XCHART statement creates cumulative sum control charts from subgroup means or individual measurements. You can create these charts for one-sided cusum (decision interval) schemes or for two-sided (V-mask) schemes. A one-sided scheme is designed to detect either a positive or a negative shift from the target mean, and a two-sided scheme is designed to detect positive and negative shifts from the target mean.

You can use options in the XCHART statement to

  • specify parameters for a decision interval or V-mask

  • specify the shift to be detected

  • specify the target mean

  • specify a known (standard) value for the process standard deviation or estimate the standard deviation from the data using various methods

  • tabulate the information displayed on the chart

  • save the information displayed on the chart in an output data set

  • read parameters for the cusum scheme from a data set

  • display a secondary chart that plots a time trend that has been removed from the data

  • add block legends and special symbol markers to reveal stratification in process data

  • superimpose stars at each point to represent related multivariate factors

  • display vertical and horizontal reference lines

  • modify the axis values and labels

  • modify the chart layout and appearance

You have three alternatives for producing cumulative sum control charts with the XCHART statement:

  • Traditional graphics are produced by default.

  • ODS Graphics output is produced when you specify the ODS GRAPHICS statement prior to the PROC CUSUM statement.

  • Legacy line printer charts are produced when you specify the LINEPRINTER option in the PROC CUSUM statement.

See Chapter 3, SAS/QC Graphics, for more information about producing these different kinds of graphs.

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