Output Data Sets

Chapter Contents

SCHART Statement

Output Data Sets

OUTLIMITS= Data Set

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

Table 40.22: 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
_LCLS_	lower control limit for subgroup standard deviation
_LCLX_	lower control limit for subgroup mean
_LIMITN_	sample size associated with the control limits
_LSL_	lower specification limit
_MEAN_	process mean ( $\overline{\overline{X}}$ or $\mu_{0}$ )
_S_	value of central line on s chart
_SIGMAS_	multiple (k) of standard error of $\bar{X}_{i}$ or s_i
_STDDEV_	process standard deviation ( $\hat{\sigma}$ or $\sigma_{0}$ )
_SUBGRP_	subgroup-variable specified in the SCHART statement
_TARGET_	target value
_TYPE_	type (estimate or standard value) of _MEAN_ and _STDDEV_
_UCLS_	upper control limit for subgroup standard deviation
_UCLX_	upper control limit for subgroup mean
_USL_	upper specification limit
_VAR_	process specified in the SCHART statement

Notes:

The variables _LCLX_, _MEAN_, and _UCLX_ are saved to allow the OUTLIMITS= data set to be used as a LIMITS= data set with the BOXCHART, XCHART, and XSCHART statements.
If the control limits vary with subgroup sample size, the special missing value V is assigned to the variables _LIMITN_, _LCLX_, _UCLX_, _LCLS_, _S_, and _UCLS_.
If the limits are defined in terms of a multiple k of the standard error of s_i, the value of _ALPHA_ is computed as
F_S( _LCLS_/ _STDDEV_)+1-F_S( _UCLS_/ _STDDEV_)
where F_S(·) is the cumulative distribution function of the standard deviation of a sample of n observations from a normal population with unit standard deviation, and n is the value of _LIMITN_. If _LIMITN_ has the special missing value V, this value is assigned to _ALPHA_.
If the limits are probability limits, the value of _SIGMAS_ is computed as ( _UCLS_- _S_)/e, where e is the standard error of the standard deviation of n observations from a normal population with unit standard deviation. If _LIMITN_ has the special missing value V, this value is assigned to _SIGMAS_.
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 SCHART statement. For an example, see "Saving Control Limits" .

OUTHISTORY= Data Set

The OUTHISTORY= data set saves subgroup summary statistics. The following variables are saved:

the subgroup-variable
a subgroup mean variable named by process suffixed with X
a subgroup standard deviation variable named by process suffixed with S
a subgroup sample size variable named by process suffixed with N

The subgroup mean variable is included so that the data set can be reused as a HISTORY= data set with the BOXCHART, XCHART, and XSCHART statements, as well as the SCHART statement.

Given a process name that contains eight characters, the procedure first shortens the name to its first four characters and its last three characters, and then it adds the suffix. For example, the procedure shortens the process DIAMETER to DIAMTER before adding the suffix.

Subgroup summary variables are created for each process specified in the SCHART statement. For example, consider the following statements:

   proc shewhart data=steel;
      schart (width diameter)*lot / outhistory=summary;
   run;

The data set SUMMARY contains variables named LOT, WIDTHX, WIDTHS, WIDTHN, DIAMTERX, DIAMTERS, and DIAMTERN.

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 Summary Statistics" .

OUTTABLE= Data Set

The OUTTABLE= data set saves subgroup summary statistics, control limits, and related information. The following variables are saved:

Variable Description

_ALPHA_ probability ( $\alpha$ ) of exceeding control limits

_EXLIM_ control limit exceeded on s chart

_LCLS_ lower control limit for standard deviation

_LIMITN_ nominal sample size associated with the control limits

_S_ average standard deviation

_SIGMAS_ multiple (k) of the standard error associated with control limits

subgroup values of the subgroup variable

_SUBN_ subgroup sample size

_SUBS_ subgroup standard deviation

_TESTS2_ tests for special causes signaled on s chart

_UCLS_ upper control limit for standard deviation

_VAR_ process specified in the SCHART 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= option, respectively, or with the corresponding variables in a LIMITS= data set).
The variable _TESTS2_ is saved if you specify the TESTS2= option.
The variables _VAR_, _EXLIM_, and _TESTS2_ are character variables of length 8. The variable _PHASE_ is a character variable of length 16. All other variables are numeric.

For an example, see "Saving Control Limits" .

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