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:

• Traditional graphics are produced by default.

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

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

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