PROC SHEWHART: Output Data Sets

The SHEWHART Procedure

Output Data Sets

OUTLIMITS= Data Set

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

Table 13.55 OUTLIMITS= Data Set
Variable	Description
_ALPHA_	probability ( $\text{[math]}$ ) of exceeding limits
_CP_	capability index $\text{[math]}$
_CPK_	capability index $\text{[math]}$
_CPL_	capability index $\text{[math]}$
_CPM_	capability index $\text{[math]}$
_CPU_	capability index $\text{[math]}$
_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 ( $\text{[math]}$ or $\text{[math]}$ )
_S_	value of central line on $\text{[math]}$ chart
_SIGMAS_	multiple ( $\text{[math]}$ ) of standard error of $\text{[math]}$ or $\text{[math]}$
_STDDEV_	process standard deviation ( $\text{[math]}$ or $\text{[math]}$ )
_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 enable 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 $\text{[math]}$ of the standard error of $\text{[math]}$ , the value of _ALPHA_ is computed as

$\text{[math]}$

where $\text{[math]}$ is the cumulative distribution function of the standard deviation of a sample of $\text{[math]}$ observations from a normal population with unit standard deviation, and $\text{[math]}$ 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 $\text{[math]}$ , where $\text{[math]}$ is the standard error of the standard deviation of $\text{[math]}$ 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 32 characters, the procedure first shortens the name to its first 16 characters and its last 15 characters, and then it adds 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, DiameterX, DiameterS, and DiameterN.

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 ( $\text{[math]}$ ) of exceeding control limits
_EXLIM_	control limit exceeded on $\text{[math]}$ 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 $\text{[math]}$ 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 _EXLIM_ and _TESTS2_ 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.

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