EWMACHART Statement: MACONTROL Procedure

Overview: EWMACHART Statement

The EWMACHART statement creates an exponentially weighted moving average (EWMA) control chart, which is used to determine whether a process is in a state of statistical control and to detect shifts in the process average.

You can use options in the EWMACHART statement to

  • specify the weight assigned to the most recent subgroup mean in the computation of the EWMAs

  • compute control limits from the data based on a multiple of the standard error of the plotted EWMAs or as probability limits

  • tabulate the EWMAs, subgroup sample sizes, subgroup means, subgroup standard deviations, control limits, and other information

  • save control limit parameters in an output data set

  • save the EWMAs, subgroup sample sizes, subgroup means, and subgroup standard deviations in an output data set

  • read control limit parameters from an input data set

  • specify one of several methods for estimating the process standard deviation

  • specify a known (standard) process mean and standard deviation for computing control limits

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

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

  • superimpose stars at points to represent related multivariate factors

  • clip extreme points to make the chart more readable

  • display vertical and horizontal reference lines

  • control axis values and labels

  • control layout and appearance of the chart

You have three alternatives for producing EWMA charts with the EWMACHART statement:

  • ODS Graphics output is produced if ODS Graphics is enabled, for example by specifying the ODS GRAPHICS ON statement prior to the PROC statement.

  • Otherwise, traditional graphics are produced by default if SAS/GRAPH® is licensed.

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

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