IRCHART Statement: SHEWHART Procedure

Output Data Sets

OUTLIMITS= Data Set

The OUTLIMITS= data set saves control limits and control limit parameters. The following variables can be saved:

Table 18.19: OUTLIMITS= Data Set

Variable	Description
`_ALPHA_`	Probability ( $\alpha$ ) of exceeding limits
`_CP_`	Capability index $C_{p}$
`_CPK_`	Capability index $C_{pk}$
`_CPL_`	Capability index $CPL$
`_CPM_`	Capability index $C_{pm}$
`_CPU_`	Capability index $CPU$
`_INDEX_`	Optional identifier for the control limits specified with the OUTINDEX= option
`_LCLI_`	Lower control limit for individual measurements
`_LCLR_`	Lower control limit for moving ranges
`_LIMITN_`	Number of consecutive measurements used to compute moving ranges
`_LSL_`	Lower specification limit
`_MEAN_`	Process mean
`_R_`	Value of central line on moving range chart
`_SIGMAS_`	Multiple (k) of standard error of individual measurement or moving range
`_STDDEV_`	Process standard deviation ( $\hat{\sigma }$ or $\sigma _{0}$ )
`_SUBGRP_`	Subgroup-variable specified in the IRCHART statement
`_TARGET_`	Target value
`_TYPE_`	Type (estimate or standard value) of `_MEAN_` and `_STDDEV_`
`_UCLI_`	Upper control limit for individual measurements
`_UCLR_`	Upper control limit for moving ranges range
`_USL_`	Upper specification limit
`_VAR_`	Process specified in the IRCHART statement

Notes:

If the limits are defined in terms of a multiple k of the standard errors of $X_{i}$ and $R_{i}$ , the value of _ALPHA_ is computed as $\alpha =2(1-\Phi (k))$ , where $\Phi (\cdot )$ is the standard normal distribution function.
If the limits are probability limits, the value of _SIGMAS_ is computed as $k=\Phi ^{-1}(1-\alpha /2)$ , where $\Phi ^{-1}$ is the inverse standard normal distribution function.
The variables _CP_, _CPK_, _CPL_, _CPU_, _LSL_, and _USL_ are included only if you provide specification limits with the LSL= and USL= options. The variables _CPM_ and _TARGET_ are included if, in addition, you provide a target value with the TARGET= option. See Capability Indices for computational details.
Optional BY variables are saved in the OUTLIMITS= data set.

The OUTLIMITS= data set contains one observation for each process specified in the IRCHART statement. For an example, see Saving Control Limits.

OUTHISTORY= Data Set

The OUTHISTORY= data set saves individual measurements and moving ranges. The following variables are saved:

the subgroup-variable
an individual measurements variable named by process
a moving range variable named by process suffixed with R

Given a process name that contains 32 characters, the procedure first shortens the name to its first 16 characters and its last 15 characters, and then it adds the suffix.

A variable containing the moving ranges is created for each process specified in the IRCHART statement. For example, consider the following statements:

proc shewhart data=Steel;
   irchart (Width Diameter)*Lot / outhistory=Summary;
run;

The data set Summary contains variables named Lot, Width, WidthR, Diameter, and DiameterR.

Additionally, the following variables, if specified, are included:

BY variables
block-variables
symbol-variable
ID variables
_PHASE_ (if the OUTPHASE= option is specified)

For an example of an OUTHISTORY= data set, see Saving Individual Measurements and Moving Ranges.

OUTTABLE= Data Set

The OUTTABLE= data set saves individual measurements, moving ranges, control limits, and related information. Table 18.20 lists the variables that are saved.

Table 18.20: OUTTABLE= Data Set Variables

Variable	Description
`_ALPHA_`	Probability ( $\alpha$ ) of exceeding control limits
`_EXLIM_`	Control limit exceeded on individual measurements chart
`_EXLIMR_`	Control limit exceeded on moving range chart
`_LCLI_`	Lower control limit for individual measurements
`_LCLR_`	Lower control limit for moving range
`_LIMITN_`	Number of consecutive measurements used to compute moving ranges
`_MEAN_`	Process mean
`_R_`	Average range
`_SIGMAS_`	Multiple (k) of the standard error associated with control limits
Subgroup	Values of the subgroup variable
`_SUBI_`	Individual measurement
`_SUBR_`	Moving range
`_TESTS_`	Tests for special causes signaled on individual measurements chart
`_UCLI_`	Upper control limit for individual measurements
`_UCLR_`	Upper control limit for moving range
`_VAR_`	Process specified in the IRCHART statement

In addition, the following variables, if specified, are included:

BY variables
block-variables
symbol-variable
ID variables
_PHASE_ (if the READPHASES= option is specified)

Notes:

Either the variable _ALPHA_ or the variable _SIGMAS_ is saved, depending on how the control limits are defined (with the ALPHA= or SIGMAS= options, respectively, or with the corresponding variables in a LIMITS= data set).
The variable _TESTS_ is saved if you specify the TESTS= option. The kth character of a value of _TESTS_ is k if Test k is positive at that subgroup. For example, if you request all eight tests and Tests 2 and 8 are positive for a given subgroup, the value of _TESTS_ has a 2 for the second character, an 8 for the eighth character, and blanks for the other six characters.
The variables _EXLIM_, _EXLIMR_, and _TESTS_ are character variables of length 8. The variable _PHASE_ is a character variable of length 48. The variable _VAR_ is a character variable whose length is no greater than 32. All other variables are numeric.

For an example, see Saving Control Limits.