PROC CAPABILITY and General Statements

Overview: CAPABILITY Procedure

This chapter describes several statements that are generally used with the CAPABILITY procedure:

  • The PROC CAPABILITY statement is required to invoke the CAPABILITY procedure. You can use this statement by itself to compute summary statistics.

  • The VAR statement, which is optional, specifies the variables in the input data set that are to be analyzed. These are called the analysis or process variables. By default, all of the numeric variables are analyzed.

  • The CLASS statement, which is optional, specifies one or two variables that group the data into classification levels. A separate analysis is carried out for each combination of levels, and you can use the CLASS statement with plot statements (such as HISTOGRAM) to create comparative displays. [6]

  • The SPEC statement, which is optional, provides specification limits for the variables that are to be analyzed. When you use a SPEC statement, the procedure computes process capability indices in addition to summary statistics. Furthermore, the specification limits are displayed in plots created with plot statements that are described in subsequent chapters.

You can use the PROC CAPABILITY statement to request a variety of statistics for summarizing the data distribution of each analysis variable:

  • sample moments

  • basic measures of location and variability

  • confidence intervals for the mean, standard deviation, and variance

  • tests for location

  • tests for normality

  • trimmed and Winsorized means

  • robust estimates of scale

  • quantiles and related confidence intervals

  • extreme observations and extreme values

  • frequency counts for observations

  • missing values

You can use the PROC CAPABILITY and SPEC statements together to request a variety of statistics for process capability analysis:

  • percents of measurements within and outside specification limits

  • confidence intervals for the probabilities of exceeding the specification limits

  • standard capability indices and related confidence intervals

  • tests of normality in conjunction with capability indices

  • specialized capability indices

In addition, you can use options in the PROC CAPABILITY statement to

  • specify the input data set to be analyzed

  • specify an input data set containing specification limits

  • specify a graphics catalog for saving traditional graphics output

  • specify rounding units for variable values

  • specify the definition used to calculate percentiles

  • specify the divisor used to calculate variances and standard deviations

  • request legacy line printer plots and define special printing characters used for features

  • suppress tables

You can use options in the SPEC statement to

  • provide lower and upper specification limits and target values

  • control the appearance of specification lines on plots

  • control the appearance of the areas under a histogram outside the specification limits


[6] You can use the COMPHISTOGRAM statement to create comparative histograms without applying classification levels to the overall analysis.