Output Data Sets

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BOXCHART Statement

Output Data Sets

OUTLIMITS= Data Set

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

Table 32.25: 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
_LCLM_	lower control limit for subgroup median
_LCLR_	lower control limit for subgroup range
_LCLS_	lower control limit for subgroup standard deviation
_LCLX_	lower control limit for subgroup mean
_LIMITN_	nominal sample size associated with the control limits
_LSL_	lower specification limit
_MEAN_	process mean (value of central line on box chart)
_R_	value of central line on R chart
_S_	value of central line on s chart
_SIGMAS_	multiple (k) of standard error of $\bar{X}_{i}$ or M_i
_STDDEV_	process standard deviation ( $\hat{\sigma}$ or $\sigma_{0}$ )
_SUBGRP_	subgroup-variable specified in the BOXCHART statement
_TARGET_	target value
_TYPE_	type (estimate or standard value) of _MEAN_ and _STDDEV_
_UCLM_	upper control limit for subgroup median
_UCLR_	upper control limit for subgroup range
_UCLS_	upper control limit for subgroup standard deviation
_UCLX_	upper control limit for subgroup mean
_USL_	upper specification limit
_VAR_	process specified in the BOXCHART statement

Notes:

The variables _LCLM_ and _UCLM_ are included if you specify CONTROLSTAT=MEDIAN; otherwise, the variables _LCLX_ and _UCLX_ are included.
The variables _LCLS_, _S_, and _UCLS_ are included if you specify the STDDEVIATIONS option; otherwise, the variables _LCLR_, _R_, and _UCLR_ are included. These variables are not used to create box charts, but they allow the OUTLIMITS= data set to be used as a LIMITS= data set with the XRCHART, XSCHART, MRCHART, SCHART, and RCHART statements.
If the control limits vary with subgroup sample size, the special missing value V is assigned to the variables _LIMITN_, _LCLX_, _UCLX_, _LCLM_, _UCLM_, _LCLR_, _R_, _UCLR_, _LCLS_, _S_, and _UCLS_.
If the limits are defined in terms of a multiple k of the standard error of $\bar{X}_{i}$ , 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 defined in terms of a multiple k of the standard error of M_i, the value of _ALPHA_ is computed as $\alpha=2(1-F_{med}(k,n))$ , where F_med(·,n) is the cumulative distribution function of the median of a random sample of n standard normally distributed observations, and n is the value of _LIMITN_. If _LIMITN_ has the special missing value V, this value is assigned to _ALPHA_.
If the limits for means 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. If the limits for medians are probability limits, the value of _SIGMAS_ is computed as $k=F_{med}^{-1}(1-\alpha/2,n)$ , where F_med^-1(·,n) is the inverse distribution function of the median of a random sample of n standard normally distributed observations, and n is the value _LIMITN_. 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 BOXCHART statement. For an example, see "Saving Control Limits" .

OUTHISTORY= Data Set

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

the subgroup-variable
a subgroup minimum variable named by the prefix process suffixed with L
a subgroup first-quartile variable named by the prefix process suffixed with 1
a subgroup mean variable named by the prefix process suffixed with X
a subgroup median variable named by the prefix process suffixed with M
a subgroup third-quartile variable named by the prefix process suffixed with 3
a subgroup maximum variable named by the prefix process suffixed with H
a subgroup sample size variable named by the prefix process suffixed with N
a subgroup range variable named by the prefix process suffixed with R or a subgroup standard deviation variable named by process suffixed with S

A subgroup standard deviation variable is included if you specify the STDDEVIATIONS option; otherwise, a subgroup range variable is included.

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 BOXCHART statement. For example, consider the following statements:

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

The data set SUMMARY contains variables named LOT, WIDTHL, WIDTH1, WIDTHM, WIDTHX, WIDTH3, WIDTHH, WIDTHR, WIDTHN, DIAMTERL, DIAMTER1, DIAMTERM, DIAMTERX, DIAMTER3, DIAMTERH, DIAMTERR, and DIAMTERN.

The variables WIDTHR and DIAMTERR are included since the STDDEVIATIONS option is not specified. If you specified the STDDEVIATIONS option, the data set SUMMARY would contain the variables WIDTHS and DIAMTERS rather than WIDTHR and DIAMTERR.

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 can be saved:

Variable Description

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

_EXLIM_ control limit exceeded on box chart

_LCLM_ lower control limit for median

_LCLX_ lower control limit for mean

_LIMITN_ nominal sample size associated with the control limits

_MEAN_ process mean

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

subgroup values of the subgroup variable

_SUBMAX_ subgroup maximum

_SUBMED_ subgroup median

_SUBMIN_ subgroup minimum

_SUBN_ subgroup sample size

_SUBQ1_ subgroup first quartile (25^th percentile)

_SUBQ3_ subgroup third quartile (75^th percentile)

_SUBX_ subgroup mean

_TESTS_ tests for special causes signaled on box chart

_UCLM_ upper control limit for median

_UCLX_ upper control limit for mean

_VAR_ process specified in the BOXCHART statement

The variables _LCLM_ and _UCLM_ are included if you specify CONTROLSTAT=MEDIAN; otherwise, the variables _LCLX_ and _UCLX_ are included. In addition, the following variables, if specified, are included:

BY variables
block-variables
symbol-variable
ID variables
_PHASE_ (if the READPHASES= option is specified)
_TREND_ (if the TRENDVAR= 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 k^th 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 _VAR_, _EXLIM_, and _TESTS_ 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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